The short version: remove your credit card from your account. Click: "Edit Account" then the click the blue "Account" tab. Near the bottom of the page you'll see "Your Payment Methods", go ahead and click the X to remove any cards you have stored. We will no longer be able to charge your card because it will no longer be stored with us.
Since hubs are shared resources you may not want to pay for the hub but someone else on the hub may wish to foot the bill.