Can I get my overpayment that my employer took from my check

I was garnished for back federal taxes and made arrangements with the IRS before the first garnishment was to hit. The IRS sent an "eFax" to my employer on Wednesday to reduce my garnishment to the $65.00 a week, Friday is payday. The original garnishment was about $350.00 and that's what my employer withheld. My paycheck deposit dropped AFTER the notice to only withhold $65.00 but they still withheld the full $350+ and state that they cannot return it to me. Do I have any recourse for getting that extra nearly $300 back from my employer?