Child Support Not Recording Payments

Ive recently found out from the mother of my child that they haven't record some payments. How do I see detailed information. If its not recorded and they are saying I still owe it what are we as fathers to do? Where do they get their numbers? And if they get them and I have proof that they aren't being recorded then what. I owe arrears, so how much of that arrears is actually owed? Thank you very much.