This may be more of a legal question, but I'll take an uneducated stab at it. Since the account was in fact closed, I don't believe you are entitled to fees. If checks came in, they'd have simply been returned. The customer however received goods/services. If the chargeback doesn't work, I'd consider the amount and potentially going after the customer for undue enrichment.
By the way, have you contacted the customer, will they pay any amounts due and make this discussion moot? It is their responsibility to one of you in any case.
My opinions are not necessarily my employers.
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell