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Hey there, welcome to the community!
Are there any other email addresses you could have used to register with Spotify? It's worth checking those inboxes to see if you have any Spotify emails--that will mean your extra account is registered with that email.
However, if you have trouble finding it, you can use the contact form to get in touch with someone from the payments center to check this for you. Make sure to reply to any automated emails you receive after you've sent the form, even if it's a no-reply.
Hope this helped!