Check this out.
My account was due to run out of time today so I waited for it to freeze and then put in my prepaid credit card information, they took it, and my account was back open. A few minutes after getting back on I was booted back off and it told me I was out of play time. When I went back to the account management page it told me that my account was once again frozen and I needed to add time to continue playing.
02/29/2008 00:03:29 SVC CHG NSF SIGNED
BLIZZARD ENT*WOW SUB
BLIZZARD.COM
Terminal: 003286 -$ 14.99
Time to get ahold of the Billing Department. =\