Because the customer stated she would complete a dispute form, your teller should have recognized an oral error claim and forwarded the information on the claim to your investigation team immediately. Your teller needs retraining and/or your procedures need correction.
If the teller told your customer at the time of the initial contact that she would have to provide a written notice of the error, and the customer failed to do so within 10 business days, you've escaped the requirement to provide provisional credit. But you have not escaped the requirement to promptly resolve the claim.
If you cannot resolve the claim on a same-day basis, I recommend providing provisional credit (even though it's apparently not required here), and lighting a fire under this case to get it resolved quickly.
Then, I'd figure out why the teller didn't perform correctly. Your procedures are inadequate, your training is lacking, or the teller had the right instruction but failed to follow it. Correct what's wrong on a going-forward basis, and move on.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8