Are you trying to modify the arrears (money owed) because you think the depository has not reconciled payments correctly? If so, then it's a Motion to Correct Arrears.
If, however, you are saying the child support amount awarded each month was incorrectly calculated, then it would be a Supplemental Petition to modify Child Support.
Note: The information presented at this site should not be construed to be formal legal advice nor the formation of a lawyer/client relationship.
Many years ago on one day, the clerk of the court gave me three different calculations of a child support arrearage, right there in Orange County. You need to get an attorney on your side.
R. Jason de Groot, Esq., 386-337-8239