Answer:
If a consumer makes a timely error claim with your institution under section 1005.11 disputing recurring transactions, your institution has an obligation to complete an investigation and provide the consumer a refund for those transactions for which your institution is unable to verify an authorization. Timely, of course, means the transaction appeared on a statement of the account delivered no more than 60 days before the consumer files the claim. However, even if the consumer's claim involves older transactions that are not covered under section 1005.11, you must still investigate to determine whether those transactions were authorized, and, if you cannot determine they were authorized, apply section 1005.6(b)'s three-step determination of the consumer's liability for those transactions (if no loss or theft of an access devise is involved, the first two steps are not used).
There is no "statute of limitations" on such transactions, so you go back as far as the earliest transaction under the consumer's claim or dispute.
In your scenario, it is possible the consumer authorized charges to their account (via debit card or direct debit) starting last July, but revoked that authorization four months ago. That's worth verifying, because there would be no need to investigate more than the most recent four months' charges. You can ask the consumer if they have any documentation of the revocation or cancellation of their Amazon Music subscription (but you cannot compel your consumer to produce it). If the consumer provides such evidence (an email or web notice from Amazon Music acknowledging the cancellation, for example), you will refund any of the the charges posted after the date of the cancellation.
If the charges were direct debits (ACH debits), your institution can return the most recent debits (no more than 60 days old). If the charges were made via the consumer's debit card, you may pursue whatever chargeback procedures that are available to you to recover funds you return to the consumer.
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