I'd research how to send a DMCA takedown request. Basically saying "This is my content and I request you stop sharing it publicly on your platform, here is proof that I own the copyright", but with a bunch of fancy legal wording added. If they don't comply after that, and you really want to go into it, you could take further legal action against them. If you're based in the US, then copyright is no joke here. May also be a good idea to get more traffic toward your actual work. But take this advice with a grain of salt, not sure if PMC likes legal advice nor am I a lawyer.