Receive a call several times a day, no one replies, then the call disconnects. Caller ID shows unknown name. I have called back and a recorded message allows you to add your number to the Do Not Call List, problem solved.
Well, no, because the DNC isn't a call blocker so it can't keep scammers who could care less about breaking the law from calling you. Invest in a real call blocker or at the very least, don't answer calls from numbers you don't recognize and don't call numbers back "just to find out who called." If they don't leave a message, they aren't worth your time.
Or do what I do: use Google Voice to call them back and don't respond to there questions. It's even funnier if you have the TV on Justice TV when you do it. I figure I'll tie one of their agents up every time they call me.