Message left that IRS had lawsuit, Called back and didn't understand accented man.  HUNG UP IMMEDIATLY

Called me twice.  Both times left a message about a "case file" and if I wanted to learn more call them back at this number.

They left me a message twice saying "on our department number (number)" but each was different. don't think I should call them back..

If they say they're IRS/are suing you, definitely a scam. In the United States(as of this writing) the IRS would contact you via mail first.
If you are getting sued, a process server (someone who delivers subpoenas/legal documents) would have shown up at you mailing address to personally give you a copy of the suit, and you would also have gotten a copy delivered via mail. So, you can freely ignore this call, and tell 'em to shove off

JUST RECEIVED A CALL FROM THIS NUMBER BUT DID NOT ANSWER