Voicemail left from 435-238-3452 said to call regarding a case file. Thanks to those who posted above - we probably wouldn't have called back but your posts confirmed what we thought.
Tell them you are Fed Agent Matt Laughton and that it's a felony to impersonate an IRS agent and attempt collection. Push at them a little and they'll hang up on you.
I have called back 12 times giving them 12 different names and info. My goal is to keep them on the line as long as possible. The last time they wanted me to wire them $7500.