All units missing from shipment?

We sent in a single box shipment at the start of September with 76 units of the same 1 SKU. This was received and all units present on 07/09/24, then on 14/09/24 all 76 units were removed from the shipment - this can all be seen on the inventory ledger under the "receipts" event type.

Seller Support won't budge at all, they're basically saying we sent in a 20kg box that had absolutely nothing in it.

We've had the odd few items go missing from shipments before, and sometimes had to absorb the loss but this is just ridiculous. We can't just lose out on hundreds of pounds because of some stupid mistake.

They weigh the boxes when they check in so how do they explain a 20kg cardboard box supposedly having nothing but thin air inside of it?

Any help on where to turn to next would be hugely appreciated.