Amazon lost my entire shipment and isn’t accepting my proof of purchase. I feel I reached a dead end here.

I’ll try to keep this simple.

About a month ago I sent 6 units of inventory to an FBA warehouse. The box said it was checked in and 6 units were received. The box was transferred, delivery stated 6 units received. I got an update a couple days later that stated that no units were in the boxes, my shipment now says -6 units.

I contacted Amazon support to start an investigation. They requested my proof of purchase stating I may not own the inventory. I sent them my receipt, the issue is the vendor I received these from does not itemize receipts, it just states (item = $x.xx). Amazon states this is not a valid proof of purchase. I am unable to get a more detailed receipt because I bought these items at a liquidation warehouse and they don’t track inventory individually.

At this time they will not further the investigation and have only suggested that I send more inventory because it is out of stock.. again not admitting it was lost at the warehouse.

If anyone has any advice please help, this is $300 worth of inventory.