Amazon lost inbound inventory

I had a shipment from overseas. The pallet was given to Amazon Freight by Estes Freight for the last leg.

My six cases of 132 products each were given to them and now, 6 weeks since the hand over Amazon says they received 18 units. Makes no sense, they would have had to open a case pack.

Anyway, I’m told I can’t dispute until June 8th but I need a signed proof of delivery. Amazon freight won’t give me that. Apparently there is no proof of delivery from Amazon freight, they can only give me a trailer number.

Any ideas on what I can do to ensure I win the claim?

Also can try I claim for retail value or is it cost?

Is there any way to get an investigation going before June 8th?