646-755-9428

Claims to be from the IRS. Left message. Don't remember exact wording, but basically I had one last chance to call them or they would come after me.  Obviously a scam. The IRS contacts you by mail.

You are absolutely correct.  This is the IRS SCAM.  You can read about it from the real IRS and news media.
https://www.irs.gov/uac/newsroom/irs-repeats-warning-about-phone-scams
http://www.forbes.com/sites/johnwasik/2016/06 ... u/#6cb8a18e171f
https://www.pindropsecurity.com/irs-phone-scam-live-call_analysis/
http://money.cnn.com/2016/05/25/news/irs-impersonators-scam/

The last link in the list is good news about some of the scammers' arrests.

IRS scam with really bad digital voice - probably because perps can't speak English.  Block.  They are now using another number -     360-928-6326 & have found away to get around no-mo-robo calls by calling three times immediately in a row.