I have managed to get past receipts from the post office but can't remember what they showed as it was many years ago. Also you need to know the time and day it was lodged and due to the time it may take staff to find it someone understanding. You may need to just write it off and you never know it may get returned to you if they could not deliver it. Just don't risk disputing it with out tracking as it will effect your sales and cost more in the long run.

Saying that I have had a few buyers ask for the tracking as it has not arrived and upon checking it shows delivered. Upload tracking and I don't hear back and to be fair they may have not checked the letterbox as smaller parcels sometimes end up there. Same as safe drop if you don't know it has arrived they may not have looked for it. Honest buyers will look and most times this has solved the issue.