Yeah, if I ever get a call from a collector I'm just going to ask them if they have my signature on a contract. If they don't they don't actually own anything and I'm free to ignore them.
Yeah, force them to take you to court and show that they own the debt. None of this "passing the paper" non-sense, there has to be a legal contract or some document saying that your debt was given to someone else. Otherwise, it's just some guy claiming you owe him money, because of "paper".