I don't know why you keep explaining that. Nobody thinks you would try to get anything you weren't ordered to get.
Find out the answer. And if it turns out he owes you more, then you have your leverage (or go after it--nothing wrong with that, either).
Have a lawyer explain it to you so you are absolutely clear about it. Maybe even ask the lawyer to put it in a letter addressed to YOU. And that way, if you decide you need it, you can mail a copy to your ex and say, "This is what my lawyer is telling me." Followed by either, "I am willing to overlook your failure to pay this, PROVIDED I receive timely payments from now on," OR, "I would appreciate your taking care of this promptly."
Seriously. And if it comes to your having to file a motion to enforce litigant's rights, you will know exactly how to state your motion.