If you call the number back, you are able to put yourself on their Do Not Call List.
Don't know if it will work or not, but I can't see any reason they would want to call someone who has clearly indicated that they will not buy from them.
Calling scammers back is just plain STUPID, and the only people who will suggest it are the scammers themselves or complete idiots, this clown is one or the other.
Oh, and if you don't understand why they would keep calling, you haven't read much of what gets written on this site. It clearly happens constantly. If you don't have clue, or you're trying to run the SCAM on here, just go the F away.
I just got a call toady and get a voice message that I have a credit card problem and as me to press 1 to speak to rep, press 2 to..... this is clearly a SCAM. Someone tells me as soon as I press 1 or 2...it will hook up to something and your phone bill will jump to the sky.... Simply just hang up.