Answer:
"Services not as described" is not one of the "errors" recognized under Regulation E section 1005.11, so you have no Regulation E compliance requirement for this dispute. That leaves you with the Mastercard or VISA network rules on assisting cardholders in disputes. If your submission of the dispute for your cardholder was timely, but past the deadline for the Mastercard or VISA network because the cardholder failed to file a timely dispute, you have no obligation to provide your cardholder credit.