Also stated I was being sued by the IRS and it was the final notice - in my case, the only notice. I came here to look for spam/scam verification and I believe I found it. Will try calling the number mentioned above tomorrow - it is 5 o'clock and I am sure no one would be in the office this late.
What office? These are scammers; there's always someone in the call center waiting for a sucker to call back, validating their phone number by doing so. Don't be that sucker. You'll just open yourself up for more grief from them and their cohorts.
Don't answer if they call again, don't call back, don't press any button to be "removed from the list" because it means nothing.
Read all the posts in this and other threads about the IRS scam.