To cancel a subscription to Avast, log in to the order portal of Avast and manage auto-renewals. Deleting or uninstalling Avast software does not cancel your subscription but only stops usage of the product.
To disable the Automatic Renewal service, log in to the Avast website. Fill in the required credentials including the order number and the password, then click Find Order. Click the Manage Subscriptions button next to the Avast product for which the subscription is being cancelled, and then select Off next to the Automatic renewals. Select Disable automatic renewal to confirm that you want to stop automatic billing.