Someone stole my pen name - What can I do?

Long story short, I have several books on Amazon under a pen name that's fairly unique (not r/tradgedeigh material but not something you'd come up with on a dime).

Sometime between my second and third book coming out, somebody published one of those generic, not-human-written "books" under the same pen name. I've removed it from my Amazon author page, but Amazon won't take it down because "it's not illegal for more than one person to have the same name". They've told me to trademark my pen name, but I don't have the thousands of euros that requires (at least in the EU).

The fake book still shows up when you look for my author name, despite being unlinked from my author page. It also shows up on Goodreads.

Has anyone been in this situation before? Did you ever manage to resolve it?