A customer paid for a service. I "Received Payment" to account for this.

Due to a series of unfortunate events, it turned out that the Invoice in question was already fully paid. It has been reconciled and the books were closed. The Invoice or the Payment can't be edited.

The overpayment was refunded to our customer.

I entered a "Refund Receipt" to account for the refund.

However, the credit on customer's account remains, and it cannot be attached to the refund in any way.

Now the customer has outstanding Credit AND a processed refund on their account. This is one of many cases, sadly. How do I correctly account for this regrettable situation now that I find myself here?