I'm experiencing this same issue. I paid for Premium and when I log into my account in a browser it says that I have premium, however, when I log in using my Android phone or my Desktop Spotify in OSX then it tells me that I still need to upgrade.
I have the same problem that many people in this thread also has, although mine isn't solveable by login in and out. I just bought Premium a few minutes ag, but it keeps telling me I need to buy Premium to use it on my phone. I've had it before without issues, but this time it doesn't work. Please help. Thank you in advance.