Billing for web hosting is deducted automatically at the beginning of each billing period. Once a bill comes due, the system will try to charge the credit card on file, and then send an email. In most cases, this email is simply to tell you that an amount was billed, and you will see that you have a balance of $0.00 at the bottom of the email.
However, if you receive an email that states there is an outstanding balance, and you see a negative amount at the bottom, further action may need to be taken. To correct this:
1) Log into your control panel at https://cp.websitesource.net/ If you need help recovering your password, select "LOST PASSWORD?" and enter your username. The password will be emailed to the address on file. If you no longer have access to this email address, or you do not have your username, please feel free to contact support.
2) Proceed to "Billing Info" (fifth icon from the top, second from the left, look for the bag of money). In here, you may need to update or re-enter your credit card. Remember to double-check the address and email on file in here, as well. Click "Submit" once you are done.
(This is still being worked on; I'm sure I forgot something important. Mostly just testing the system right now.)