To update the credit card information on your account, you must contact the billing company you signed up with by telephone. Here is their contact information:
NetBilling
Email: helixstudios@netbillingsupport.com
Phone: 1-(866)-268-0652 (From US and Canada toll Free)
International: 1-(661)-621-9181
CCBill
Web: http://www.ccbill.com/customer-service.html
Email: consumersupport@ccbill.com
Phone: 1-(888)-596-9279
Do not send credit card information via email, this is not a secure way to send your data. If for some reason you cannot make the phone call, simply sign up a new account.