The IRS would send you a letter they would never call anyone that's the first clue.
I got the same call 10 min ago I did not answer it it went to voice mail I put the number into caller ID and it said this... Morales, Connye#
They keep on calling from this number, and occasionally leave a warning message about my troubles with the IRS. Fortunately my system blocks this number after one ring, except the times they leave a message.