Good thinking! I have been getting these calls from various numbers for years. Since I pay my 2 cards off every month, I'm not paying any interest and the stupid calls never specify what card they are calling about. I have seen many reports from folks who don't even have any cards. Best bet is not to answer any calls from numbers you don't know and if a message happens to be left, check here first and don't return call if it is suspicious!
I did the same thing. When asked which card he was referring to, he would not answer. I asked him why is he calling if he can't specify which card. He finally said, "ma'am, have a good day" and hung up.