(a) The commission may not consider adjusting the amount of a fee due the commission under this code or the Health and Safety Code:
(1) before the fee has been paid in full; or
(2) if the request for adjustment is received after the first anniversary of the date on which the fee was paid in full.
(b) A person who pays an amount that exceeds the amount of the fee due because the commission incorrectly calculated the fee or the person made a duplicate payment may request a refund of the excess amount paid before the fourth anniversary of the date on which the excess amount was paid.
(c) A request for a refund or credit in an amount that exceeds $5,000 shall be forwarded for approval to the commission fee audit staff, together with an explanation of the grounds for the requested refund or credit. Approval of a refund or credit does not prevent the fee audit staff from conducting a subsequent audit of the person for whom the refund or credit was approved.