My son has just purchased NBA league pass for $379!!! How can i reverse this as it has already been direct debited from my account? please help!

Hi Jimbo,

For any issue with a purchase that was made through the iTunes Store or any other store that Apple has, take a look at the article below to walk you through getting your issue sorted out.

Report a problem with an item purchased from the iTunes Store, App Store, Mac App Store, or iBooks Store

http://support.apple.com/en-us/HT204084

Take care,

-Norm G.

In addendum to already sound advice, you may with to consider setting up restrictions on your AppleTV to avoid potential repeat occurrences. You can lockout features or purchases with a PIN.

Apple TV: Understanding Restrictions (parental controls) - Apple Support