VISA's chargeback timeframe is the later of 120 days from the date of transaction or 120 days from the date of promised delivery provided the promised delivery date does not exceed the transaction date by more than 540 days.
Since your customer is beyond 120 days from the transaction date, you will want to request proof of the promised delivery date such as a contract or invoice. You may also request that the cardholder first contact the merchant in an attempt to resolve the dispute. If this is not successful, the cardholder should write a letter outlining their effort to resolve the dispute with the merchant and the merchant's response and include supporting documentation for the delivery date.
Since Reg E does not apply here, if the cardholder cannot satisfy the requirements for you to file a chargeback on their behalf, you have no further obligation to the cardholder.
_________________________
Sola Gratia, Sola Fides, Sola Scriptura, Solus Christus, Soli Deo Gloria!
www.tcaregs.com