First, find out whether the customer is claiming that none of the charges were authorized, or only the last X charges. In other words, was the deduction never authorized, or was it authorized at first, but the authorization was canceled at some point. Then investigate by contacting the company initiating the entries. Maybe you'll be able to confirm that some of the transactions were unauthorized. Let's assume that the transactions starting with the one in September 2016 were unauthorized. Figure out when the statement showing the September debit was sent to the customer (or made available if held or e-delivered). Start with that date (statement sending date) and determine the date that is 60 calendar days later. That is the date before which the bank is accountable to the customer and any of the debits posting after that date are the customer's responsibility (because she had a responsibility to check her statements and notify you of unauthorized transactions so that you could prevent future unauthorized debits from the company).
If the lady is slipping into dementia, this is not going to be an easy task for you.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8