Open a ticket :). No need to do so until you get a ticket from us about it, as we open several tickets. If you've not gotten your card by the 3rd, you'll get a ticket from us titled "Please Update Your Billing Information", to which you can reply asking for an extension. In almost all cases, we're happy to grant one. Once you get your new card, just update your card information in the Linode Manager, submit your payment, and then update the billing ticket. Generally painfree :).
-Doug