As stated in the terms of service you must use our client center to cancel your service. It is the only method to protect from
your account getting deleted without your knowledge. This assures (and you) that only the account owner (or someone the account owner has delegated) can cancel your service.
To request a cancellation, login to our client center, locate the package you'd like to cancel, and click on the "gear" icon. Then choose "Cancel Package" and select when you'd like your package canceled.
If you have difficulty, you may also submit a support ticket requesting cancellation.