xbox gamertag has randomly changed & gamerscore...

well since your name doesn't seem to be random with a gamerscore of 5363

you cannot

only randomly generated names within the first 30days of creation can change their gamertags for free

only during specials are the gamertags for 400ms points

your gamertag has Zero gamerscore, it seems to me you accidently have created 2 gamertags and named them similarily. this could easily be caused if you had used 2 different email addresses (for example by typo and then afterwards correct email).

xbox Support can help you sort out if this is the case.

if you recieved a forced gamertag Change by xbox your gamertag would have been randomly assigned with a combination of 2 words and a number like "NameChange12345", not just your current gamertag -1 Digit

Hi there,

If you're not showing a gamerscore reset on your account
https://enforcement.xbox.com then you've probably just been hit with a glitch that has been randomly effecting users. And it just happened to take place when you changed your gamertag.

With the glitch, the score will return in a few days.

Hello,

This "free" gamertag change is only available if you made your gamertag on either XBOX.com or on the XBOX 360 console itself and received a randomly generated gamertag (Example: FuglyDuckling10 - randomly generated gamertag). This "free" gamertag change is
only available within the first 30 days of the account being created, otherwise you would be charged 800 Microsoft Points for the gamertag change.

So since you have already changed your gamertag and it is not a randomly generated gamertag you would have to pay the 800 Microsoft Points fee just like everyone else.

The gamertag you have now is not a randomly generated one so it has been changed at some point.

Any other changes then you will have to pay.