I have got hacked by someone before. Simply call microsoft. Make sure you give them all your account info that you know of. (They will probably ask all the questions.)

The biggest thing is that you have the Xbox 360 Serial Code (I think that's what it is) found on the back of the console or I'm pretty sure it is also found on console info somewhere by the console settings on the dashboard. This will show that the account was made on that Xbox. If your account was made on another Xbox, I'm pretty sure you still will have to give Microsoft your code just to show that your hacked gamertag was active on that Xbox for awhile.

I hope this helps. I got my account back within 7 days. However, I seriously got hacked. I didn't willingly give up my email/pass. I would suggest that you lie to Microsoft and say you got hacked by someone talking trash in an Xbox Live party. Just say that you played a kid in a game of MW2 and he invited you to a party afterwards and when you joined he was threatening to hack your account. A few hours later when you tried signing in, it said that your account information was invalid.

Simple. I hope you get your account back man. It really sucks when you are trying to do a favor for someone and they steal your account and be a dick like that. PM me if you have any questions!!

Your friend probably Stole your acc.

License transfers were Patched though