Child support and additional child care expenses are separate issues. You appear to be asking whether for each dollar you pay toward care expenses your support should be reduced by a dollar. No, that's not how it works.
If you were ordered in the divorce judgment to pay for health insurance, then that's what the order provides. If you believe that the support order was miscalculated based upon your wages and the premiums deducted therefrom, you can seek a review. Some states limit how often reviews are permitted.
The probation department prepared a new income withholding order, which presumably was signed by the judge. Take a look at your copy of the order. Signed by the judge?

