You can ask your ex- to pay you the money. You can sue your ex- for the money. You can seek relief through the divorce court, with the relief available depending upon the terms of the judgment or your ability to enforce the judgment. Keep in mind that you are only going to get money from your ex- if they in fact have money. If they fell behind on the mortgage because they're dead broke, even with a court order for reimbursement... as they say, you can't get blood from a stone.

If it can be done consistent with the order and state law, it may be time to petition for the sale of the home. If your ex- can't afford to live there, the court may be receptive to the idea.