Same exact thing happened to us! Hahha They actually blocked us from calling them, since we turned the tables and started calling them non stop. (it's free minutes, why not!)
Did not answer when the number appeared on caller ID. A voice message recording stated it was the IRS with final notice of a lawsuit being filed; no other information provided. Requested a call to the same number. I know people who work for the IRS. That's not how they operate.
Called my landline and left a recorded message. States that it is the IRS calling and they are about to begin a lawsuit against me. Must call back immediately