My account name changed

It's possible that your gamertag was changed by the enforcement team if it violated the ToU/CoC. If so it should show on the enforcement site HERE

If this is the case then you gave your permission for this when you started your account & you would have to pay to change the tag to something else.

so its prob so person i kept killing in battlefild...

If you want to find out why you'll need to ask here:
forums.xbox.com/.../41.aspx

They won't tell you who filed the complaint, I don't believe you can change it for free after a forced change, but the e-mail you should have received will likely say for sure. It wasn't changed until now because no one complained until now.

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community.

Hello FuhaedAlshammari, the Gametag exchange system is automatic, if when choosing a Gamertag the system shows this message it means that it is not allowed by community rules and By Microsoft.

In this case you need to choose another name or write it in a different way.

This thread is a year old,in future you need to start your own thread.

Doesn't matter if it's your mothers maiden name,if it breaks the code of conduct then it will not be allowed.

You need to post in the forum fredgiblet linked to find out what part of the CoC it violated or read the email sent to the address linked to your account.

You will not be able to change it back to the original tag.