Please ask your lawyer to form a letter about the copyright of the book. He needs to mention the course sales on Taobao are not legal. You need to sign at the end ofthe letter.
I would also like to ask for a authorisation letter if possible. This would help me deal with this matter. I am glad to help you on this.
Ask your lawyer to write a letter about the course of copyright, the letter should mention courses currently sold on taobao violations, letters have your handwritten signature. Also, if you can, I hope you can give me a written authorization, authorize me to deal with this matter. As an English fans, I am very happy to help you.