Royal Mail Parcels have a 16 Digit Doorstep Delivery Code on your Proof of Postage. You can use that to Confirm Delivery as long as you enter it into Dispatch.
Do you have a Royal Mail Proof of Postage for the missing Item? If so enter the 16 Digit Code into Track and Trace. Does it say Delivered? Just add that to the Ebay Item Not Received Case if your Buyer does indeed Open a Case?
