Sorry to hear about the trouble. Just to confirm, have you tried refreshing your music library from here: Google Play Music > Menu > Settings > Refresh? Also, let us know how are you accessing Play Music (browser/ iOS /Android). Keep us posted!
Thanks for trying those steps. Let's try clearing the app's cache from here: Settings > Apps > Google Play Music > Storage > Clear cache > Restart. Also, please make sure that you're running the latest version of Play Music app. Keep us posted!