Fact: it has happened before
And also similar has happened to me, my contract with orange was due to expire so i went with another company however, without my permission my contract with orange was renewed and for 3 months i never used it once nor did i know it was renewed then I had to pay the 3 month bill.
Under 18 or not, you dont need to be over 18 to be liable to pay your debts lol!
If you have a service our mistake or not you are liable to pay for it unless you notify them. End of the day it will prob just get cut off, but that doesnt mean you are not liable to pay for the service you had.
it has happened before, looked it up, its happened with a few people.
your phone contract is totally different, you didnt read the small print, iv got an orange contract and if you dont inform them that you do not wish to renew your contract then they automatically renew it, whereas with microsoft you are not gettin tangled in a contract, you pay for 3months and then they cut you off after 3months and if you wish to pay for more months you have to subscribe for gold membership again, if you dont it doesnt get carried on.
yes they can send him a bill out asking him to pay for the last year n half that he's had free, but he has every right not to pay it and theres nothing they could do to make him pay it as it was a mistake of their own and there is no small print saying "if your live is still enabled after the subscription expires please contact microsoft otherwise you will have to pay for however long your live is enabled"
if they had said that then yes they could make him pay, but unlucky for them they havnt and so he has free xbox live and they cant do jack other then cut it off, which they probably wont as its all automated and they probably dont get someone to go through the millions of accounts checking to make sure they are disabled when their subscription has run out.