If the customer contacted the bank to report his receipt of the credit from the merchant, you can annotate the file to that effect and mark it closed. If you provided provisional credit, follow the routine steps for reclaiming it, including the provisions about covering overdrafts. I recommend sending a written confirmation to the customer (copy retained) reporting the action you're taking.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8