" I do have a problem and would like to know how to file for more money on him.
let me know who is the best person and guide me through these steps."--->I guess, Your question is more of a legal question than a tax question. Whether, or not, your ex-spouse just pays the full amount which he owes you is a legal question. You may want to notify the court of his noncompliance with the court order, that is the divorce decree, I guess, and support order or etc, if this has not been done thus far.