Ask HN: A company used my source code for their product. What can I do?

Context:

- My source is a library that this company shamelessly copy/pasted into their product (whose source is also publicly available) without even giving me credit.

- This library is a core component of one of their (I would go so far to say it IS one of their) products.

- My source is publicly available BUT it's not licensed, hence it's still considered under exclusive copyright (see https://choosealicense.com/no-permission/)

- Both I and that company are in the EU.

Normally I would never enforce anything like this but we're talking about a company that was funded using public funds (Horizon 2020) and is now making money from basically selling my library.

I want to make money out of this. Any suggestions on how I should proceed? Thanks.