iTunes credit
Why is my credit card being charged when I have an iTunes credit?
If your balance is up-to-date and you've bought things and your credit card was charged, contact iTunes Support : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)