If you mailed your payment it will take longer for the payment to arrive, USAA processes credit card payments on the day that they are recieved. Might I suggect that if you have access to usaa.com that you use the WebBILLPAY. It's is fairly simple and straight forward. You can review the payment information to make sure that the payment has been processed, pending or completed. I use it to pay my USAA accounts and its been awesome...
From USAA.com, Log in.
I hope this helps...
I am sorry to hear about teh available credit on your credit card was not updated to your satisfaction.
Some possible reasons for this:
As per the credit card agreement USAA may have placed a temporary hold on the availability of the funds on the card. This is done to ensure that the credit card payment clears in full as some payments require further verification (hold on electonically payed accounts tend to be held for up to 7 calendar days from when the hold was initialized, and are generally available for use on the 8th calendar day, But this may be held longer depending on how the payment was submitted.) To confirm this and when the funds would become ready for use you might call USAA credit card servicing and see when the funds will be available.
The second is the one that DSTexas mentioned, that there may be authorizations that have been processed and or not yet released or aged off the account. Pending authorizations only effect the available credit and may stay on the account for up to 15 days(although they generally fall off after 7 days)
Either way - I am sorry that you were caught off guard.