Gamertag Mistake

It all depends if you choose a gamertag thats already been used. Thats the reason you getting the #0000 at the end. New gamertag system is a bit similar to discord username, those #0000 are there so you can have any gamertag you want without adding extra
characters or random words to come up with a unique gamertag.

Limited time to fix errors, not a complete edit. You could have a confirmation message saying gamertag blahblah will be permanently changed within X time, please review and edit mistakes.

As they have said its not possible unless you pay for another change.

Unfortunately not. Only the first change is free and now if you need to change your gamertag you will need to pay the fees.

The #0000 at the end are part of the new gamertag system. If you don't want the numbers to be displayed at the end of your gamertag then you'll have to come up with a gamertag thats unused by anyone. Any unused gamertags will not have the #0000 at the
end, so if you don't want the numbers, keep trying different gamertags until you find one that isn't already taken.