I can understand that this is frustrating for you. Have you browsed through the information in LawInfo's Free Legal Resource Center to learn more about your issue yet? See:
http://www.lawinfo.com/consumer.html. You should certainly try to speak to a lawyer to determine what legal options may be available regarding petitions for contempt and how long you have after the children are 18 to file. In the meantime, you may be able to learn more on your own. Search the "Free Legal Resources" tab, or browse the Consumer Resources. Good luck.