Tonight, due to a time-zone related issue, the e-mailed invoices were sent out before the credit card batch process was complete. This meant the first invoice you received tonight may have shown an owing balance on your account (if you are paying month-to-month from your credit card).
The second invoice you received would have included the credit card payment, and the actual, correct account balance.
Rest assured, your credit card was only billed once- you can simply disregard the first e-mail invoice.
We apologize for any confusion this may have caused.
If you have any questions or concerns, please reply let us know.