Visa/Mastercard rules state that the bank is required to take steps to prevent "unjust enrichment." Since you cannot utilize the chargeback process to return the funds to the merchant, you are required under V/MC rules to make a good faith effort to contact the merchant to make arrangements to return the funds to them (e.g. mailing them a cashier's check.) If you are unable to contact the merchant, the funds would eventually be escheated in the merchant's name as unclaimed property.
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