How do I net off Unallocated Receipts against Unallocated Payments?

I raised a proforma sales invoice to a customer for £7920.00. They paid the amount and until I raised a VAT invoice for the actual amount, I placed the payment in trade debtors and the amount was visible as an unallocated receipt.

The amount sold was slightly less than intended and so the VAT invoice was only for £7502.40 - ie less than the proforma payment. So once I entered the VAT invoice, I went to unallocated cash and allocated £7502.40 of the £7920.00 against the invoice, leaving £417.60 still as an unallocated receipt.

The customer asked for the £417.60 back. I transferred the amount and when explaining in bank imports, put it as a refund to the customer. However the transaction has gone as an unallocated payment.

So on the Unallocated Cash screen (Money>Bank Accounts>Unallocated cash) I now have £417.60 in unallocated receipts and also £417.60 in unallocated payments.

If I look on the transaction report for all transactions against that customer, the closing balance is zero.

How do I clear the unallocated receipt and unallocated payment - they net off to zero so I should be able to get them off my unallocated cash screen?