The procedure will depend upon the payment gateway that you used.
For Credit/Debit Cards:-
Please write to firstname.lastname@example.org with details regarding the payment gateway used and we will further assist you.
You can directly do that from the PayPal account. Please follow the instructions below for canceling the PayPal subscription.
Go to Settings.
Click Payments near the top of the page.
Click Manage Automatic Payments.
Select the merchant whose agreement you want to cancel, and click Cancel.
Click Cancel Profile to confirm your request.