I have a project on GitHub licensed under MIT. Some other person contributed to another unknown-to-me organisation on GitHub two months ago with a commit which copies a part of my code with just a few, very minor, line changes. This commit also adds another license and has no mention of me and my copyright statement and my license (so, of the original project). I also noticed him having other commits like "Copy some more libraries" what clearly is a malicious intent in my opinion, as this has been done more than just once. Initially I wanted to contact this person, but then noticed the same pattern with other projects where he adds another license (so he knows about licensing!), removes parts of the original code, sometimes changes the code, sometimes doesn't, and even names it similarly. After I noticed that pattern, I decided it would be silly to ask him to follow the licenses as he, most likely, understands what a license is as he licenses his code himself.
What can I do in such a situation if I don't want this person to continue stealing other code from everywhere and licensing it on his terms like it is his own and make him follow the original project's license terms?