Since this has been happening ALL the time this year, I don't answer calls when unknown numbers. No message left, googled it and saw all these posts. Caller blocked! (remember the IRS DOES NOT contact you via telephone, they are too busy for that! Plus they need a paper trail...)
I get at least 3 calls a week. I tell them I am on the do not call registry and "Alex" says "okay, I will call you tomorrow " and hung up. How do I report to the FCC?