SOP for Procurement and AP on Vendor Return

I'm struggling to find the accurate process for both purchasing and accounts payable to process a return. Our issue with our current process is that our purchasing team will process a return in PO31 for an item. The credit will then be processed by accounts payable and will keep the PO closed. When the replacement item comes in, AP attempt to match to the same PO as referenced on the invoice and they will receive an error that the credit can not be processed on a closed PO.

I feel that there is something simple that we are missing and was hoping that someone could send me their SOP's for Purchasing and AP so that I can see where our issue lies.