So, I've had problems recently with getting people that I don't know following my playlists - in general, I don't want people following them, because Spotify doesn't tell us who follows our playlists (Hint: Spotify, please fix that.... if someone's gonna follow my playlist I wanna know who they are) but I ESPECIALLY don't want people I don't know following them, especially people who follow my account and who I can't block (Hint: Spotify, please fix that too).
Anyway, for anyone else having this problem, here's how you keep strangers from seeing your music:
1. Don't publish your activity
Even if you don't publish your activity, however, they can still see your playlists, so this doesn't completely solve the issue. Here's how you stop allowing people to follow a playlist or set of playlists:
1. Create a copy of the playlist(s) that you want unfollowed. You do this because even if you hide the one they're currently following, they'll still see it. After they follow it, they'll see it whether you hide it or not.
2. Make sure you have all the songs from the original playlist in the new one, so that you don't lose anything.
3. Delete the old playlist, and make the new one private. Now you have all the same songs on a new playlist, and no one can follow it, because it's hidden.
Yes, it's a little bit time consuming, especially if you have a lengthy description for your playlist, but believe me, it's worth it, because it gets rid of those followers that you don't want.
Hope this helps anyone who had this same issue! :)