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Have you tried logging out and back into your account on your device as this will work as a refresh where it may update to premium.
If not try getting into contact with the @SpotifyCares team on Twitter with a direct message or emailing them to see if they can assist in any possible account recovery!
Hope this helps! 🙂
Ah okay, the support team will be able to help.
The teams email: firstname.lastname@example.org
The teams twitter: @spotify OR @spotifycares