How to file complaint against Amazon as a seller

I sold a book to a buyer who provided an address that was a warehouse or business address. I shipped it via USPS. A week or so later, the buyer filed a claim saying they didn’t receive the book. When I contacted USPS to ask about the tracking, they said that the address was a business where an agent picks up all the mail and distributes to the workers at that business. The buyer claimed they never received it, the USPS tracking says “delivered to agent for final delivery,” and Amazon A-to-Z still refunded the buyer and penalized my account. Amazon claims that the tracking shows they lost the book just because it doesn’t say in big green letters DELIVERED. Now it says my account is at risk of deactivation. I only sell a few books and this one “order defect” gives me a 33% defect rate. This is absolutely ridiculous! I did everything correctly and I not only lose money and the item I sold, but my account gets penalized. I should’ve be punished for shipping the book to the address I was provided. This is the worst business practice ever. I’ve already appealed the claim and Amazon is still refunding the buyer and penalizing my account.

Where do I submit a complaint about this? I’m thinking the Better Business Bureau and Federal Trade Commission? Any better ideas?