Okay, so here's the situation. My brother created an Xbox Live account somewhere in 2009 or 2010. The Microsoft account that's linked to was used solely to create his gamertag. He didn't use the Microsoft account for anything else.
As time passed, he began to lost interest in console gaming, and didn't play Xbox Live for over a year.
However, now that we have Grand Theft Auto V, my brother suddenly wants to get on Xbox Live again. When he signs in, he is greeted by the new security proof message telling him to sign in with his Microsoft account email address and password. He knows the email address, but he doesn't know the password. (I think my brother was still on hiatus when the new security proofs system was implemented and might have not been aware of it.)
We've tried to recover the account using the online account recovery form, but it asks for things such as the subjects of the emails sent. My brother never sent any emails with the Microsoft account. It also asks for credit card information, but he never charged a credit card to his account (for Xbox Live Gold).
I don't know what to do now. Is there anything I can still do? Or is my brother S.O.L.?