The customer has the right to claim fraud and the bank needs to investigate. At the end of the day, the bank should evaluate any losses incurred, the relationship with the consumer and whether a card should be issued to them at all. Giving approval and then reneging on that is easily justification to me.
View the claims and any possibility that the consumer did the transactions, authorized them, or benefited from them. If they did, deny the claim. If they did not, review the immediate approval process the customer gave when contacted and make a decision - was it easy for the consumer to be mistaken or negligent, or is this buyers remorse and the transaction asked about was approved.
If you feel confident the consumer approved the transfer when spoken with, I would strongly consider denying the claim. I would attach both together if they were in the same claim and period when done unless there is evidence otherwise. It is a subjective case but the law puts the burden on the bank.