"If a different gamertag is showing when you sign in to your account it means it is a...

well the old gamertag has been link to another email and that email is a hacker , so i cant recover it

Hi crixzoid!

Please be informed that in order for us to start the account recovery process, we must know the correct email address that's linked to the gamertag or Xbox profile you're trying to get back into.

I suggest that you check your email history including your spam or junk folder or archived emails to find traces to which email address your Xbox profile was linked to. If you still have your old consoles like Xbox 360 or Xbox One, etc where your account was previously added, you may check it if you could see the email address of your account there.

You may as well check it on https://account.live.com/username/recover by entering a phone number or email address which might be possibly linked to the account you're currently looking for.

Hi, when you sign into the xbox change the email on the gamertag that comes up then hopefully when you recover your account again using the same email the second gamertag should show up.

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Steps how to change your email through the xbox here:
support.xbox.com/.../switch-gamertag-to-different-microsoft-account

That means the email that you signed in with on your brothers account was not the same email associated with your gamertag what you want to do is check on your xbox in settings under the account tab and sign in security and passkey and it will show you the
email associated with the gamertag.

But do you sign in with the correct Microsoft account? It shows you a random gamertag?

If you sign in to the Xbox website with the same Microsoft account, does it show you a different gamertag?