Had authenticator on account for as long as I can remember, and my credit card information shouldn't have been available to them either :S
Apparently your CC info is stored in your account, or else Blizzard couldn't charge it. Anyone who hacked your account could very well just use the battle.net function in your account to renew the sub.
And stop with the paranoia... Like others said, go ahead and call Blizzard, clear it up. if all else fails initiate a chargeback with your credit card issuer.
Chargeback: When providing proof to your credit card issuer about an transaction that was not authorized by you, the transaction will be reverted, you get the money back, and the business that charged the transaction gets hit with an additional fee, which is usually around 20-25 USD.
So, Blizzard should be, and usually is, very interested to avoid chargebacks for that matter alone. Additionally, if chargebacks occur rather frequently then they are penalized as a risk business. Which creates even more inconveniences for Blizzard to do that kind of business.
So, no. Your suspicions are pointless on all levels.