you should have received a copy of the notice to withhold. read it. it tells you that you have so many days, not a lot, to file a petition to challenge its accuracy. do so and send a copy to the employer.
It seems that the only error is that there is no termination date in the amount withheld for arrears. That is actually fairly typical. You can seek a modification of the order so that your employer knows when to terminate the amount for the arrears but if the interest is only $.06, that part of the order is not worth pursuing. Please seek the services of a lawyer if you cannot handle this yourself. The modified withholding order must go through the court system before it is served on your employer.