If you're on Premium, try signing out and back into the app.
If it says Free, check the receipt we send to your email inbox. Make sure you're signing in with the username on that receipt. If the username on your receipt is a 10 digit number, please sign in with your Facebook login details.
It's also possible you have a second account - one account with a Spotify username, the other created and linked to your Facebook profile. Try logging in with each to access your Premium.