If you aren’t certain about the details you used to register on the app, go to
password reset and enter possible email addresses you own. When you enter an email that's registered with Spotify, you'll get a password reset message for that email.
Note: Keep in mind there are a few ways to sign up, e.g. with email, phone number, Facebook, Apple, or Google. Try logging in with these, your Premium account may be linked to one of these options as well.
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