My account was Hacked?

[user-removed]

I have not logged into my spotify account for a long while, I used to log in regularly but my device was having a problem using my speaker so i unninstalled and quit premium.

Now i am reinstalling the app onto my new chromebook, and all of my playlists are gone, along with my daily mixes and song history and have been replaced with a bunch of stuff i have never listened to. 

I have already logged out of all devices through my account page, but how did this happen? How do i prevent it from happening again? and most importantly, what is going to get done about any of this?