Subscriptions acquired from special promotions do not need to be canceled, as free subscriptions do not auto-renew.

If your paid subscription was extended via a special promotion, you can cancel your paused subscription that is set to resume after your free promo extension expires by visiting your account settings and clicking the Billing button on the left side of the screen. Next you'll click Cancel Renewal.

On the next page, click Cancel your subscription. This will prevent your subscription from being resumed/renewed.