Someone selling under my listing

Hello guys, In the last few months i started to sell items on amazon. I’ve done brand registry and everything. I’ve noticed couple weeks ago that someone is selling under my listing, and he’s obviously not selling my brand. It’s the same product basically but not same quality and not branded. I’ve tried to file a report on amazon but they keep telling me to report through brand registry, but there i can report only if he uses my brand to sell, which he not. How can i solve it and get him off my listing as i try to always get the highest quality and paying for advertising? Thanks in advance