random songs and artists being added to my music library

Every so often I'll find songs in my Music library that indicate that they've been purchased. There's even a complete album. The thing is that none of these have been purchased. At present there are 21 songs. If I try to delete them from the library all that happens is that they get hidden.

I have no playlists that are being automatically updated, so these songs aren't tied to that. They aren't even from artists or genres in which I have any interest.

Any ideas what's going on, how to stop it, and how to get rid of these things from my account?

Although I'm currently on Sequoia (15.3) this started happening well before I upgraded.