I've come across this before, but in that instance, the author knew what the problem was. She'd published chapters on medium. All she had to do, was to write a letter to herself explaining that she is the copyright holder of the online material, giving herself permission to publish the same material in the book as is already available online. Then send the letter to Amazon. The problem was then resolved. Have you published a chapter on Medium, or samples on your website? Or anything else? Because this is what you need to do.