Manual Debit Memo quantity error

Hello;

We have a situation where we received an item on a standard PO.  This item was billed and the invoice was paid by AP.  The item was later Returned to Supplier, however, the team did not check the create Debit Memo box and so no DM was created.   Now the Shipment status for this PO line is "Closed for Invoice".  The Ordered quantity shows 1, the received quantity shows 0, and the billed quantity shows 1.  The purchasing team wants to close/cancel this PO because the quantity still shows 1 is ordered.  We tried creating a manual Debit Memo for