Hello @CamilaCasabona, thanks for writing!
My first suggestion is that you check if you have a second Spotify account for some reason.
So when you click on the link bellow, does it show as Free or Premium?
Note that you can also see your past receipts on the left column (if you're using the Spotify desktop app).
If it doesn't clear things up, you could try using other devices to make the payment.
Hope this helps!
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Note: I'm not a Spotify employee.