You can use the "totality of information" available to you in your investigations, including the consumer's transaction patterns, etc. If you have what you believe is conclusive documentation that several of the disputed transactions were, in fact, completed by the consumer, I think you have enough reason to conclude that the consumer might be "mistaken" or "misinformed" concerning the earlier transactions, especially if the older transactions were completed at machines or locations where you have evidence the consumer completed some of the later transactions.
All of which is a "polite" way of suggesting that the consumer's entire claim is fraudulent. I suggest that you have enough here to deny the claim, cancel the card(s) and ask the consumers to take their account(s) elsewhere.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8