I think my account got hacked and is being used somewhere else. How do I put a stop to this?

Agreed. I wish they'd acknowledge a problem here. I'm very careful online, don't sign up for random things or click links in e-mails (especially the junk e-mail accounts I use for things like Live) etc. so I definitely was not phished. My info was compromised
somewhere be it MS, EA or somewhere else linked to the account (can't think of anything else that would be linked up unless my hotmail just got hacked--but Live is the only place I've had any fraud issues).

^ Exactly. The ONLY reason you got "hacked" is because you use the same user/pass with other sites as you do for your XBL sign in. Someone managed to get ahold of your info elsewhere and guessed at it on probably 100 other sites until they get into one.
Someone playing a game against your can't hack your account info while you are playing lol, that's complete bs to the goof balls saying it / agreeing with it.

To put it simply, you got "hacked" because you screwed up somewhere, period. Change user names and passwords every few months or so and for your sake, NEVER use the same user/pass as you do for online banking or low level sites that probably get hacked
/ messed with a lot. I have been with XBL since beta and have always had a CC on file and have never once had an issue.

You are the reason you got hacked, be more careful and stop putting blame where it shouldn't be. 45 huh? Then you should know allllll about the "it's NEVER my fault" game lol, it always someone else or something elses fault :|

I had a match today with a Christmas NOOB who kept whining about his explosives getting hacked.

-

*Noob dies*

Noob: "OMG! I got killed with my own explosive!"

Me: "Yeah, that happens."

*Noob dies."

Noob: "OMG! It happened again!"

Me: "So stop using your bouncing betties."

Noob: "Why should I?"

Me: "Because the enemy's hacking them."

Noob: "They can do that!?"

Me: "Yes, they can."

Noob: " How?"

Me: "With a PDA."

Noob: "What's a PDA?"

Me: "A device that's used to take hack enemy explosives."

Noob: "How do I get 1?"

Me: "By leveling up & unlocking it with an unlock token."

*Noob dies*

Noob: "OMG! Stop hacking my explosives!"

Me: "Stop using your explosives & they won't have anything to hack."

Noob: "But I wanna use my betties!"

Me: "I don't think that's a good idea..."

*Noob dies*

Noob: "OMFG!"

*Noob dashboards*

*Game ends (Noob was host)*

Everybody else: "OMGWTF!"

Quick question, did it say you were signed in somewhere else? That is a sign of a hack. When I was hacked, I also got disconnected often, so do not take this lightly. While it MAY be what ngocphi says, it could also be a hack.

Still theft from xbox stopping ppl from accessing there digital purchased games and dlc it's disgusting how they steal your games like this

Well, your account was hacked...so they likely put a ban on it to stop the other person from using the account (much like a bank would put a stop on a stolen credit card)..you would then contact them (appeal in this case) to get them to re-open the account if you have full control of it again. At least, to me, it seems that would be the most sensible thing for them to do upon being informed an account had been hacked