If their calling about a credit card account, then I would look into your credit report just to be sure no one got a credit card in your name. And if your credit is good then these people are just trying to get money from you. And they'll go as far as threatening you with arrest warrants, etc. I would report them to the FTC and block the number. And never speak to them again! Talking to them and arguing about it just makes them wanna call you even more!
Yeah, sounds like a scam to me, too. Gotten this call a couple of times now. Even leaves a recorded voicemail message (when I don't answer the call because I see the non-local area code) saying they will call back later for "service verification."