by Ken Golliher:
We don't usually hold court here; the issue is whether or not a judge would agree with you, not whether one of us would.
Regardless, your proof seems to be more than adequate. I would put through entries that would correct the original transaction, not just debit the account for the amount due. Then write the customer a very brief letter explaining the correction and noting your prior attempts to reach him by phone.
Timing is of the essence here; it will eventually dawn on this customer to simply close the account and reap the windfall. Posting in the Guru Forum vs. a public forum will delay your receiving a response by days or even weeks.
by John Burnett:
Here's an update on this drama. We contacted the individual who asked the question, and learned that the bank's customer apparently listened to his or her conscience (after realizing the evidence the bank had of the overpayment) and returned the $1,200. There is one very relieved teller, who undoubtedly learned a lesson from this mistake.