Mrthdrb

I had a first round telephonic interview with a company - I thought the interview went very well and I was hoping to hear back from them by now, but I haven't received any call yet.

Whenever I call HR they are not taking my call. I saved the number of the interviewer who had called me, so shall I directly call the interviewer to follow up, or is this considered unprofessional?

From email career.alert@comname.com I got a schedule email with one link "Cancel" if timing is not Ok, date and time etc.

HR called me to check mail and asked to be available on time. There was no follow up, contact number or interview process.

Here I am specific like should I call interviewer or not instead of how to proceed for the follow up.

*Company: This is a big company with 10000+ employees

I had saved interviewer number who had called me for interview so can I directly call to interviewer to just follow up or it is not professional?

Do not do that. (Assuming that "directly call to interviewer" indicates the number you saved is more of a personal /desk number and not the main office number)

You are supposed to follow up with the HR / recruiter. Unless you were told explicitly to get in touch with the person who interviewed you, you have no business calling them back and asking for updates.

That's why a usual telephonic round ends with something along the lines of "The HR/ recruiter will get in touch with you". I'd be surprised if this was not the case for you.

If the number you saved is a common office number (listed on their website / job post), then you can call up that number and ask to transfer your call to the hiring / recruitment department (if applicable) to directly to the recruiter/HR - but not to the person who interviewed you.

That said,

When I am calling HR she isn't attending my call

is not a very good or positive sign. Some people are really poor in communication, especially when communicating a negative response. Somehow they feel ceasing all communication is the best way to communicate. If I were you, I'd give a couple more attempts at reaching them, then move on.

That depends on the way in which you got the phone number for the interviewer. While uncommon, I wouldn't rule out completely that you simply said "can I follow up with you directly after the interview" and the interviewer said "sure, here's my number". In that case, the interviewer has welcomed you to contact him after the interview directly, so you shouldn't feel bad about doing so.

If, however, the interiewer didn't give you their number for this purpose, or, worse yet, if the interviewer doesn't know you have their number, then absolutely do not do this. It's like trying to go through a backdoor, and giving your possible-future coworker trouble because of it. Even if you get the job, that's not likely to look good for you.

If HR isn't picking up your calls, then probably you didn't pass the interview. Keep looking. If you got this interview through a third-party recruiter, you might want to let them know you've been "ghosted" (that's the term for what seems to be happening to you); ghosting is very unprofessional behaviour and your recruiter may have some words for the company if they're doing this. You may also want to leave a review on a job search site like Glassdoor about this company as well, because of this unprofessional behaviour. Otherwise, there's not a lot you can do but keep looking.

(US-Midwest perspective. Your mileage may vary.)

If it's been a week then yes you can call for a quick 'I'm checking in to see how the job search is going.', as there could be a hundred reasons why you haven't been contacted yet, such as they've already ruled you out, they're still interviewing, they've offered the position to somebody else and am waiting for their answer, they're waffling on if they really need the position, they're waiting for somebody to come off of vacation, they're waiting for a senior person to be available so they can schedule a final interview, who knows.

One of the best jobs I've ever had I did that after a week of silence, and the hiring manager response was 'What? They should have offered you the job three days ago! Give me an hour...', and I had the job offer in my Inbox in 20 minutes.

Good luck.
Jim

Do not call them directly.

One of the reasons for HR departments and recruiters to exist is that they are supposed to handle your application, and the point of a phone interview is to get a quick gauge of a candidate without spending too much time on every applicant. Whoever called you for your phone interview called you only for that phone interview, and will not want to be hassled with further unsolicited calls from yourself, when they might be in the middle of something else - unless they explicitly told you that you could.

All else being equal, the most likely reason they've not got back to you is that they have decided not to continue with your application for some reason. (This may not be as a result of anything you've done wrong - they may simply have already filled the position). It is impolite of HR not to respond to your calls, but that kind of rudeness to an unsuccessful candidate is, sadly, not uncommon.

However, if HR are not responding to your attempts to follow-up...

If HR have not responded to your calls and emails for a significant length of time (definitely more than a week - at least two would be better - their HR staff may simply be on holiday for example), it is possible that something has gone missing between the interviewer and you, and it might be worth finding another way to follow up. (Note the disclaimers. This is possible, but less probable than that you're not still being considered).

In that case, you might consider sending an email to the interviewer if you have their address, or can find it on a public site (e.g. the company's website, or LinkedIn). Unlike a phone call, this places no demands on their time (they can just press "Delete" if they don't want to talk to you) so even if they find your persistence annoying, it will be low-level annoyance and forgotten quickly.

Do not try to "guess" at their email address or start looking up their non-business social media profiles. If you can't find their email as public company-related information, they clearly do not want to be contacted and you should not do so.

I would say that the answer really depends if you got this interview from an agency or not.

If you did get it via an agency, then as per Sourav Ghosh's answer, your contact is the agent; and you should be asking them. Calling the company directly would be unprofessional until you have got to the point where you are planning to discuss contracts and the agent has released your contact details to each other.

If you didn't get it via the agency, but HR are not answering the phone at all, then it's not a positive or negative thing at all, since they are VERY unlikely to be blocking your number - you could prove this trivially by calling from another phone. I would personally assume that HR not answering is a sign that either they're not in their office, or they're busy and unable to answer.
I personally would call the main office number and ask to speak to HR regarding a recent application and see what the reaction is - but I would certainly be continuing sending out my CV.

In either case - the interviewer will be very surprised to get your call, and may even be in another country to the office you're expecting to work in... and surprising people tends to be a negative thing.