I have had a couple of these calls. Called back on a non identifiable line assuming it was a scam call. I had to let the phone ring a long time (10 rings) and the ring was very strange (broken ring) as if it was being routed to another place. A woman answered and there was lots of noise in the background as if she was at a pay phone or sitting in a call center with lots of people talking. I didn't talk to her but she identified herself as IRS.
Beware off this scam Google IRS phone scams and see they are useing a spoof numbers in a call center looking for victims they leave a fake voice mail saying a law suit and final notice . I called the number back and it sounded a idian man said he a officer for IRS red flag saying if I don't pay today the cops will be at my door with a warrent and read me me fake charges said he sent me letters but they came back there red flag. He had a whole script down trying to scare me in any way I just hope nobody falls for it this as on the news also . Scam
total scam...first of all the only time you'll get any type of correspondence from the IRS will be through the U.S. Postal service....they never ever correspond by phone, text or email....