I cut off his spiel and said, "How did you get my telephone number? And can you please describe the 'existing business relationship' that allows you to call me even though my phone numbers are on the National Do Not Call Registry?"
Naturally, he simply hung up. I assume the instructions to these boiler-room people are to hang up if someone actually asks informed questions like mine or cites the DNCR. Of course, the Do Not Call Registry is a joke because nobody's going to enforce it by chasing down the people ignoring the law, on account of there being bigger fish to fry.
When I get sales calls from people like this, I see no reason to be polite. Other sales calls I will usually at least politely tell them, "Not interested; thanks," but these "debt relief agencies" are vultures. I know their practices, and they're scum. I can't even dredge up sympathy for the people working the front line of the boiler room when what they're doing is so slimy.