Your customer cashed a check frauduantly, regardless of what the teller should or should not have done. You have every right to get your funds back.
Do you have the item to charge back? It doesn't sound like the maker has filed a fraud endorsement at their bank, and you have not received the check back.
If you have the item, charge it back to your customers account. After charge back give your customer the check and let them deal with the maker.
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