My inventory got robbed using Amazon partner shipping

Hi all, i sended my yearly inventory for a product that i sell, it got robbed from the DHL truck in mexico city, they made me wait 2 months for me to be able to open an investigation, which i did and they keep rejecting me. I have no idea why, i attached the commercial invoice with all the data they needed, even tell my provider from china to put my FNSKUs instead of the barcodes, has all the info of the products as well as mine including my mexico tax number, also all my provider data, address, phone, name, company ETC. Also attached my ups shipping number and an screen shot of that number being delivered in my address, they still are asking me to proof ownership, i don’t know what to do, does anyone had ever needed to proof ownership? what can i be missing?