Write down their number on a post it note and flush it down the toilet, you'll get the same response from the do not call list.
Telemarketer rodeo is fun and simple, here's how to play. Get them on the line, keep them on the line, sound really interested and when you get to the credit card number part laugh in their ear and brag about how long they were wasting time on the phone with you. If everyone did their part they would lose so much money they'd actually have to work for a living.