Answer:
You can't return it because it's past the midnight deadline for returns. Since you have a stop payment on file, the check is still subject to that stop payment, and, if the depositary bank requests an adjustment, you should refuse (the depositary bank bears the responsibility for its encoding of the amount), and you have no authority to charge your customer for the difference.
Your bank should reimburse your customer for the $16 and the stop payment cost, but leave the stop payment order on your books.