FBA shipment - FBA received more than I sent?

I sent a shipment to FBA that consists of 80 units (40 units of 2 SKUs). FBA confirmed they received 40 units of 1 SKU, but 80 units of the other SKU - which means they received an additional 40 units. I have triple checked inventory on my end and I am sure that we only sent 40 units, not 80. The weights on the shipping labels also suggest so. However, upon creating a request to investigate into the "missing inventory", Amazon still confirmed that they received 80 units instead of 40.

I've tried to reach out to Seller Support also, who aren't able to help but just provides links to documentation and investigation request page.

Does anyone know what else I can do?