I had problems with renaming five chars at one time and with the subscription fee being charged for four accounts on the same day another time. After talking to bother the CC company and Blizzard, I know that this is a Blizzard issue. Blizzard allows only a certain amount, 2 or 3, charges to a credit card within a certain time frame. I guess they are giving it some time to see if it is rejected by the CC company. If you do call the Blizzard billing support, they will push your payment through manually. Watch out - they just do what you tell them, so if you ask for the 3rd payment and hang up, be prepared to call again for the 4th. =]

Any non-boxer will usually not encounter this issue, since there won't be multiple things charged to the CC in short order.