Enter the email address you used at checkout and the last 4 digits of the card you paid with. If they match an active subscription we cancel it immediately — all of them, if you have more than one. No account, no phone call.
Cancelling stops all future payments straight away. It does not delete the account you use inside the app, and it does not by itself refund a payment that has already been taken — for a refund, write to support.