Once you answered the "card services' scammers call it already verified they had reached a working number. Calling the number back will only reenforce that fact and cost you a long distance call, since they have no intention of removing your, or any other number, from their robodialer. Most of the scammer's numbers seen on the caller id can't be called back anyway since they use all spoofed (false) numbers to hide their true identity and location.
I just got a call from them. My general policy is if I do not recognize the number of the person calling, I ALWAYS let it go straight to voicemail. If it is someone I know, but using a different number, they leave a voicemail for me, identify themselves, and then I call them back.
With this one, of course, they didn't leave a message, so I googled them to find out who they are. Scammers!
The funny thing is, I don't even have a credit card. I pay for everything with cash and money orders. They were wasting their time with me anyways. They were never going to get any money out of me.
The drug-addicted "card services" scammers use all spoofed (false) numbers which makes identifying and locating them more difficult. If pending legislation passes to make the spoofing of name and number illegal, the scammers will not be able to hide,and will become easier to prosecute.