Try logging into your Spotify profile on your browser here with your email. Your username will be displayed after you login.
After that, check the status of your subscription. If everything looks ok, logout of the app in your device, and be sure to use that username, instead of your email address, to login to your account. It's the one with the Premium features.
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Did you get an email receipt for your subscription purchase? In it, it shows your Spotify username:
Logout of the app, and be sure to use it to login to your account. It's the one with the Premium features. If you see a random number, that's your actual Spotify username, which was assigned automatically to you when you created your account through Facebook. If you see it in your receipt, you need to use the Log In with Facebook button.