How can we prove that our goods were delivered?

I have recently been selling on Amazon. I applied for the high-value goods channel, which requires deliveries to be made by truck. This ensures that we get the customer's real phone number and contact them to schedule a delivery time. Sometimes, the provided phone numbers are unreachable, but we always communicate multiple times via email and phone to ensure the machine is accurately delivered to the customer.

Each delivery to the customer comes with proof of receipt. However, I have recently received two claims from customers stating they did not receive the goods. One order was over $800, and the other was over $1,200. I provided the logistics tracking information and proof of receipt to the customers and informed the claims team to verify the delivery status using the tracking numbers we provided.

After each shipment, we always provide the delivery channel and tracking number. Despite explaining the issue in detail and attaching the logistics tracking information, proof of receipt, and even delivery photos, the claims team does not recognize our evidence. They say they cannot confirm whether the goods were shipped. Do we need to go to the customers' homes to prove that the goods were delivered?

This is unacceptable. For issues of undelivered goods, the claims team only needs to check the tracking number through the channel we provided to see the logistics tracking and delivery proof, but they refuse to do so. Does CEVA Trucking Company's documentation hold no weight at all?

We have occasionally encountered customers lying about not receiving goods, but as long as we provided proof of receipt, Amazon would recognize it. However, recently, it seems they don't care. We provide sufficient evidence to prove that the customer received the goods, but they do not acknowledge it and say they cannot confirm the shipment.

This behavior of only believing the customer's word without investigating seriously harms sellers' interests. Why is this happening on Amazon? Amazon provided me with an appeal channel to verify, but they don't care. Even after appealing, they still say they can't confirm the machine was delivered, don't investigate, and even close our appeal channel.

I have opened multiple cases to report this issue, but they just forward our problem to the claims team and then there is no further response. This seriously infringes on the rights of sellers. Why is this rogue behavior happening? How can I prove my goods were shipped? How can I prove my goods were received? How can Amazon recognize sellers' rights? Do we have to file a lawsuit to protect our rights? Do the platform's policies have any effect?