Issue with Shipment Reimbursement

Hello,

I am having trouble with amazon stonewalling me for a reimbursement of a couple thousand of dollars for one product. Provide supplier invoice, showed UPS delivery confirmation/tracking numbers, and even included their own Inventory Ledger clearing showing they had received all the cases and units. Items seemed to have been lost during a FC transfer, what are some ways i can resolve this issue? I would appreciate y’all help!