I've have two cheque payments that were created by paying two invoices that I had created. These were actually supposed to be prepayments not paid against any invoices. I now have the actual invoice that I need to enter, and I would like to be able to apply the two existing prepayments to this invoice and delete the two previous invoices that are already "paid". The only way I know how to do this is to reverse the two cheque payments, delete the two erroneous invoices, then remake the cheque payments but when I do this Sage forces me to use a different cheque number since the numbers have already been printed. 

Is there any way to unapply the two payments from the invoices so they stay on the vendor account, but I am able to delete the two incorrect invoices?