The IRS never starts a collection via a phone call; they always send snail mail first! In 40 years of paying taxes I have been contacted by the IRS only twice. In one case I entered a number in the wrong field but it did not affect the outcome of the return. The other time someone put in a wrong SS number and it turned up to me. In both cases I sent a letter to the IRS (with a copy of their letter) explaining the situation, and it was resolved.
Hopefully you're being sarcastic on 'scary'. When did the 'IRS' start randomly calling people, much less threaten to sue anyone, or court dates issued by phone? The word missing before they say they're the IRS is BOGUS. What's even better is not giving them any chance to leave phony messages. They can't play with a number that only rings.