I found something that has fixed it for me (at least so far...)
I have been having seeing this issue for a few weeks, and it has burnt a hole in my data plan, so I turned off cellular data for Apple Music while I investigated the problem. Here is what I think is causing the issue for me:
Along the bottom of the screen, go to "Connect" (the symbol looks like "@")
I discovered that I was following hundreds of Artists because I had "Automatically follow artists whose music I download" turned ON...
I changed this setting to OFF, and "unfollowed" all of the listed artists.
I did this this routing several times as new artists kept popping up....
Now that this list is clear, I have had nearly a week of no unwanted music music appearing on my iPhone.
It works for me - I hope it works for you....
Good luck