my son has spent a fortune

No one from Support is here in these forums that can help with Account or Billing Issues. Not sure how he could have bought the same game twice, much less three times as the Store will tell you "You already own this". Call them or chat with them from the
Support page. That will be the only way to resolve your issue.

Hi!

Check your
order history, select the purchase and check if you can request a refund. Otherwise try to contact the
support directly.

You would need to try contacting support and speak to billing. 1-800-4my-xbox if you're in the US/Canada or http://support.xbox.com/contact-us

For refund you can first try the auto function in
http://commerce.microsoft.com if doesnt get, you will need to contact the official Xbox Support. They are the only ones that can determine if a refund is possible or not.

To contact Xbox Support use the Phone or Microsoft Support Chat option at
http://support.xbox.com/contact-us

...but Vietnam had 'Fortunate Son"......at the start of EVERY match