Timely file your return and then file a Petition for Contempt. If you are able to show that the violation was wilfull, you may be able to collect attorney fees for having to pursue this matter in court. All of that said, it is worth a call to your former spouse to see if it can otherwise be worked out before you initiate proceedings. Regardless, you should consult with a lawyer as this information should not be construed as legal advice.