Just want to clarify, but does your shuffle play work? If it does then the box is jus advertising premium to you because as a free customer you will receive ad's in the app, which include ad's for Spotify premium.
If you haven't already you may want to try premium free for a week as it may change your mind?
I see, have you made sure you have updated to the latest version of the app? Is it possible your Internet connection isn't working properly for Spotify, are you using a modified version of the app by chance?
If you can provide what phone your using and what version of IOS and Spotify you're using that would be a big help!
That's fine! If you want to check yout can do so by going into your device settings, head to General theN tap 'About Device'. Once you are there scroll down a little and you will see your version (X.X.X) I am on 6.0.1.