I wrote them a mail which was linked under "general request". I just noticed it was in even in December 2022, not January 2023.
I just wrote them again asking if they received my mail and forwarded that to their info@denic.de address. Just saw they have more contact info on their website.
If they still don't reply, I'll give them a call. I won't give up that easily haha
Nice, I at least received an automatic reply now from info@denic.de