How to correct the quantity and price on a paid invoice

Hi,

The issue we are facing is that matching an invoice to one of the POs results in an overbill.  On investigation, it was found that an invoice was matched to the PO and the invoice was subsequently paid.  However, the quantity and price entered when matching to the PO was incorrect although the invoice amount was actually correct.  What the user had done was to enter: quantity = 10; price = £41.54 and amount £415.40, instead of quantity = 1; and price = £415.40.  What is the best way to correct this issue given that the invoice has already been