I just get in contact with support. They made me to create a new account and carry everything (songs, followers, lists, premium rights..) to that new account and deleted the old one. They also gifted 6months of free premium too.
I've been having the same problem and tried every fix, nothing worked. Finally I installed the desktop version on a different PC (A PC that I've never used for Spotify), set my profile pic (Discover Weekly pic) on that PC and in about a day I noticed it changed on my other PC as well as my mobile devices!! I know not everyone has mulitple PC's to play around with but give it a shot if you can and post back.
My Facebook account is disconnected from my Spotify Account, actually I deleted my Facebook as well. I added a profile picture in my Spotify Account today and even after all this changes my Discover Weekly picture still being my old picture from Facebook Account.