First, call probation. They may be able to administratively adjust your account and send a revised garnishment.
If you and the ex get along, she can issue you a check and then you jointly sign a letter to probation reflecting this and asking the account to be adjusted.
If none of the above, then file a quick motion asking that your support obligation be reduced (depending on the amount you're paying, $25 - $100 per week) until the credit is repaid.
IF YOU LIKE THIS ANSWER AND APPRECIATE THE TIME IT TOOK TO WRITE IT, PLEASE SELECT IT AS "BEST ANSWER." Thanks. The above is said without seeing your case file and without my understanding the entirety of the facts of your case. Depending on those facts, the above information be may incomplete or may be completely inaccurate. The above is intended as general information only based on what you described and not as legal advice. I advise you to consult with counsel who may be able to provide better information commensurate with a better understanding of your situation.
You won't get that money back. Instead, the credit will be used up if probation understands the situation. You will likely need to write a letter explaining your situation.
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