Quoting Madi's*Mama:" !!!! Seriously I bet you guys would feel different if it was the other way around and they were using your money for their bills. "
This exactly!!! I also must raise the question, since she claimed it was a joint account, was it HIS card information used to pay it. Even if her name is still on the account, if she used HIS card information, it's fraud. And it CAN be traced to her because she has the phone bill account information and passwords to be able access the account and pay it. So, it's fraud, identity theft, because by using HIS information, OP was presenting herself AS her estranged husband without his permission, and paid a bill in HER name.