The Security Mentor

You already knew not to give your credit card number to someone who called you.

Now it's not safe to give your credit card number to somebody you call. Criminals are now tricking phone companies into forwarding calls away from legitimate businesses and to the fraudster's phone number. [iva Bruce Schneier's blog].

Closest you can come to protecting yourself is to check your credit card statements and complain quickly if there's anything weird.