So, let me get this straight. You published your software under a free license that stipulates they can't remove the license and are otherwise free to do as they please.

They took you by your word and did exactly that.

What did you think a license is for? For artistic expression? It's a contract. If you want to get paid, put that in your license.

I recommend AGPL 3. Then nobody will rip you off. And if they do, you can drag them to court over it.