i didn’t authorize this purchase

If you claim you didn't buy it (I assume you've changed the account's password etc. if you are saying that the account has been hacked) contact iTunes Support and see what they say : 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’)