They're probable a private debt collection company. They go around buying up bad debt from CC company or anyone/company for that matter for pinnies on the dollar, then aggressively go after the debtors for anything they can get. As long as the tactics they use aren't considered harassment it's perfectly legal and done all the time.

As far as getting your number, that's easy unless it unlisted. All they have to do is since you live across the street, go to the courthouse records with your address (most of which are on line) and look up your name (public info BTW) then use the revers phone directory and unless your number is unlisted, they have your number and can call you. you used to be able to get some ones phone number just by putting there address in to google, but I think they changed that. The DNC list doesn't apply to them cuz they are not trying to sell you anything.