Small claims court all the way. The demand letter alone should get their attention. Takes a few hours of your time - no lawyers needed.

Also contact any attorney general office in your state. Amazon pay is licensed as a money transmitter. Threaten their license to perform their business and they’ll start paying attention.

There’s a phone number on this page: https://pay.amazon.com/help/82972 of 866-216-1075 along with their license number and appropriate licensing agency for each state. My experience with obscure state licensing agencies is that they are looking for something to do - you bring them a slam dunk case and they will be happy to help and go to bat for you.

Edit- Amazon pay actually links to each state’s agency website here: https://pay.amazon.com/help/201310940

If OP is out there I’ll be happy to help.