Music Licensing Question - fanfiction and derivative works

I'm dealing with a situation and need some guidance.

fanfiction and derivative works. I've been dealing with this for about 9 months now and the situation isn't improving.

This involves original creative work over the past 11 months. I do have documentation proving my ownership and timeline.

Am I overthinking this or is this a real legal issue worth pursuing?

This happened to me too. Have you tried filing a complaint with the relevant agency? In my case they investigated and it got resolved without needing a lawyer.