The squeaky wheel gets greased.
I'd be on the horn with equifax and the credit card company. Sometimes you can write to the credit agencies explaining a problem like this and it can help. And I for sure would be speaking with whomever I had to at the credit card company to get this taken care of. Since the debt occured after your divorce, if the credit card company won't give you relief, you may want to take him to small claims court.