Credit card responsibility

I get asked occasionally by clients about Joint Credit Cards. The Question usually goes this way.
My wife and I got divorced and I keep getting calls about payment of her credit cards. I never used it but why am I involved?

You are involved because either the Credit Card was of joint nature, meaning both of you applied and both signed on the dotted line. OR You applied either knowingly or unknowingly and your wife was assigned as an authorized user.

Either way you are pretty much on the hook. On the first situation, because it is a shared responsibility not dealt with with your seperation agreement. The second.. Because regardless of seperation or marriage, your name is on the account as principle account holder.