I once allowed an artist's song to be added to one of my playlists when it got released. Now, I constantly get their songs added to that playlist but I don't know how to stop it.
Solved! Go to Solution.
Or it could be you went to an artist's website that was offering to save their new releases to your library like a pre-save option where you singed in with your Spotify account.
And revoke access to the app that may be causing it.
There will also be some apps listed from Spotify such as this Community site and a few others. Make sure not to revoke access to those.