Hi Disbursing,
According to the
Credit Info Center, a joint account holder (frex, someone who was jointly responsible for the debt, not just an authorized user) can re-open closed credit card accounts, particularly if they were satisfactorily paid prior to closure.
In most states, however, you're only responsible for debts incurred on joint accounts
during your marriage.
Your first step should be disputing the debt. Send the creditor a copy of your divorce decree, the credit report noting the date of the hard close, and the police report you filed. Explain that you closed the account, and that your former spouse re-opened it without your knowledge or consent a full 18 months after your divorce became final.
You'll also want to dispute it with all three credit reporting agencies using the same information as above.
If that doesn't help, you'll want to talk to an attorney. Good luck!