Welcome Chotofrut,
Based on your post, you can't download music from Apple Music due to an error about using too many devices. We'll do our best to help out with this.
You mentioned checking your Apple ID devices. Are you referring to checking that with these steps: Check your Apple ID device list to see where you're signed in - Apple Support
If so, that will provide you with the devices using your Apple ID. That wouldn't tell you which devices are being used with Apple Music. Do other people use your Apple ID for Apple Music? We ask because these Apple IDs are for personal use and are not meant to be shared with others.
What happens if you test a restart of your iPhone: Restart your iPhone - Apple Support
As that helps to solve many issues.
If this happens on a Mac or PC, see: Authorize or deauthorize your computer for iTunes Store purchases - Apple Support
Should it persist, what is the specific error message and what does it say? Does it say that you can't download because there are too many devices using Apple Music? Let us know and we'll continue to help.
Wishing you well, cheers.