I closed a paid off joint credit card account several years ago. The account was closed because the account was no longer needed and not due to a pending divorce. 18 months after my divorce in Texas was final, my ex called the credit card company from Iowa and reopened the zero balance closed joint account and charged $2000. I discovered this after a different credit card company mailed me a letter saying they lowered my credit line due to negative items on my credit bureau file. The company with whom I closed the account with insists that a joint account holder is able to reopen a closed account, I dont see how but cant find anything in laws or regulations to disbute.
First they recommended for me to remove my name from the account by signing their form along with my ex spouses signature but when they recieved the signed document they said the account is now a bad debt and they can no longer remove my name (the ex has made zero payments towards the account). Then they recommended I file a police report but when i called to confirm the address to send the police report they said I am still responsible.
I have proof the account was a hard close from an old credit bureau file that says "closed by consumer". How can I still be held responsible?

