Joint accounts and joint debt can be very complicated during a separation, during a divorce, and even after a divorce is finalized.  While you may have a reached an agreement with your ex that your previous joint account would be used to pay on a joint loan, the third party in which you took the loan from is not bound by your divorce agreement.  You can go to the family court where you devised your divorce agreement and have your ex held in contempt since he is not abiding by the court’s order to follow the divorce agreement.  The third party can continue to attempt to collect a debt from you if you were previously on the loan because you are still on the loan, even though you are divorced.  Additionally, you could file a claim in small claims court if you were to pay this loan to collect from your ex for him to re-pay you.  Either way you will need the court to get involved to have your ex pay this loan if he will not do it on his own.  However, the court will not be able to have a third party stop contacting you because they are not bound by your divorce agreement.