How to report design theft or plagiarism effectively?

Hello. I’ve discovered some of my designs plagiarized on Amazon. I’ve reported it using the “Report an issue with this product or seller” link, then I select “other” and explain that the design is stolen, but I feel like Amazon won’t do anything. Maybe I just need to wait some time, or perhaps it’s not the exact place to report it because “report plagiarism” or something similar is not listed among the options. Now I want to sell my own posters and sell those designs that are mine.

What can I do?