Whether there is a limit or not depends on your order. If it says there is, there is. If it is silent, then there is no limit at least while the child is under 18.
If you can prove overpayment you should be fine. Whether you can collect your expenses or not is up to the judge, but you had better have a document on file requesting reimbursement of those fees. I suggest you contact an attorney and have them help you. They can request that she pay your attorney fees as well.