Tiktok Shop Owner Keeps Selling My Art Without My Permission, Unsure Of Course Of Action (usa)

Hi all! I’m very out of my depth here and would really appreciate guidance. I’m a digital artist and sometimes I draw fanart. I do not sell my fanart online. In the last month I’ve been informed by a few people about a shop on TikTok that has stolen one of my works and is selling it on t-shirts. I reported the user back in November and TikTok shop assured me the post and item for sale were taken down. I had reported through their IPR form and included links to my original post and account to verify I was the artist. I do not use TikTok in really any capacity, but the fanart was popular enough and my style’s recognizable enough for people to let me know. But today someone contacted me to say that they still have the shirt up for sale and have multiple videos promoting it. I went through the same IPR process for the videos reporting those, but it’s been an infuriating process especially when it’s obvious the entire account is stealing art and making profit from it. I don’t think I’m within the realm to sue here, even though I am the artist I can’t stress enough that this is fanart of existing IP and not directly mine, but it’s been very discouraging to deal with especially with how many people are buying the shirts (for 20-50usd through TikTok Shop). And from what I see from my peers, TikTok in general can be unhelpful to creators and art gets stolen all the time for commercial use so I’m feeling very out of my depth and bothered that this has kept happening, especially when the poster acknowledged that I was the fanartist. So what do I do? Am I allowed to send a cease & desist? What legal course of action is available for something like this? Am I just SOL? Thanks so much in advance.

Mobile isn’t letting me go up and add but I am in the state of Nevada if that makes any difference wrt copyright/ip laws