This is a common and persistent scam. The IRS does not "call you to serve notice of a law suit"... they will send a court constable to deliver a subpoena if they are taking you to court. Have no fear of hanging up on this caller---It is total garbage. There is no reason to call them back, they will try to pressure you into making a "settlement payment" using your credit card. Silly. just block the number and ignore similar calls like this in the future.