recently bought my son a used iphone 4 and since he's had it he has run up an excessive bill which is for apps that are not on his phone and today I received a bill for £40.99 for an app that he hasn't down loaded. I know what he has downloaded as he

You've checked the account's purchase history to see if that app shows on it (and if so when it was bought) : See your purchase history in the iTunes Store - Apple Support ? And checked the phone to see if the apps are on it ?

If it shows on your account's purchase history then you can try the 'report a problem' page to contact iTunes Support and see if they will refund or credit you (but purchases are considered final) : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

If it doesn't show on your account(s) purchase history then contact your card issuer