Have you gone into it on another one of your devices? If I leave it going on my iPad, I can’t get into it on my phone. You can only use one device at a time.
The only solution, if it’s not you and you think someone else has your Apple ID , is to change your password
Change your Apple ID password
https://support.apple.com/en-ca/HT201355
You would then need to turn iCloud music back on in your devices to access it (as well as “ Show Apple Music”)
Turn on iCloud Music Library with Apple Music
https://support.apple.com/en-ca/HT204926