Yesss. I'm with the same problem. At first I didn't remember that I had log in with my facebook account. So I did another acount and updated for spotify premium. But now, I have canceled this premium acount and I'm trying to upgrade the one which is connected with my facebook.
But I'm having trouble doing this. The system is reporting error. "you have already upgraded a premium account".
So, I need to delete the one that I did and just use the account connected with my facebook (because it has all my playlists).