See also the Subscription response object.
If you want to stop billing a credit card, you can cancel the subscription. Once canceled, a subscription can't be reactivated. You would have to create a new subscription. You can't cancel subscriptions that have already been canceled.
var result = gateway.Subscription.Cancel("the_subscription_id");
If the subscription can't be found, it will throw a
The value used to identify a specific subscription. If you do not specify an ID when creating a subscription, the gateway will generate a 6- or 7-character alphanumeric ID. Once canceled, a subscription can't be edited or reactivated. You must create a new subscription.