It is incredibly unlikely that a court will retroactively change the amount of support due and unpaid in the past. What the Court can do with the correct proof is to reduce the amount of support due going forward to more accurately reflect the party's financial position. The obligor can prove the payments he's made by asking his bank for copies, front and back, of all the checks written to the ex. If she has been making material misrepresentations to the State, that is going to be a problem for her. But if there is a support order, signed by a judge that says "make payments to DCS. You will not be credited to payments made to somebody else" then arguably he had notice of where to pay.
DCS is tough to reason with. Once they decide that somebody owes support, that person really needs a lawyer. The only silver lining is that DCS won't collect back interest.
I know, cold comfort. Strongly recommend that you hire counsel to deal with this.
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