Here is another number with a recording from the IRS.  It comes up as Florida.  Please beware!  It refers you to the number 202-697-9984.

I also got a voicemail telling me it was "final notice" that I was being served with a lawsuit by the IRS. The number they told me to call was 202-697-9984.

The call originated from 446-952-7632 which is not in the United States.

I got the same robo call about the IRS as you did, from several different numbers.  Of course I knew it was FRAUD and Identity Theft and did NOT call back.  One of the numbers was not even a valid area code, another one was a FL area code but the prefix was 168, which I have never seen used before.  I blocked both numbers and have not gotten any calls in the last month or so.  Glad you did not call back and I hope nobody got reeled into this scam.