If you need to put an account on hold for any reason, find the customer in the Billing control panel and access their account. From the General tab scroll to the bottom of the page and select Put On Hold.
This will place all services on the account on hold. If you would prefer to only place a particular subscription on hold, select the Subscriptions tab instead. Click the subscription you wish to place on hold and on the General tab scroll to the bottom of the page and select Put On Hold.