How do we file an insurance claim with Fedex?

I just experienced today this same issue and I can't see how this is even legal. Fedex won't support you using any account number on the claim unless it's the one who "directly" paid for the shipment, meaning they will deny any claim where the sender uses their own account number instead of ebay, as the information doesn't match. 

If you call ebay they will NOT give you an account number or file the claim for you, or contact fedex to do so. They will only provide you links to go to fedex to download an .xlsx file which requires using an excel app to open. Once there, you have to edit the file and then email them but you still need the ebay fedex account number to do so which is not provided. It seems almost impossible to get assistance as fedex customer service won't even answer basic questions without the fedex account number, and will hang up on you if you ask for a manager. How can any company claim to provide insurance if it's literally impossible to get any assistance, let alone be able to provide a correct claim form application? It's horrible and I will probably contact the BBB about this.