Changing Gamer tag to defaults

The numbers after the # are randomly generated numbers that can't be changed. they denote that there is more than one person with that username

When you first create your account you get a default gamer tag, it's usually two names and a number altogether. You can change it once for free, which it appears you have.

Gamer tag changes have been $9.99 for years now. No way to get it for free.

ok so the only way to get a free gamertag change is if you where issued and default gamer tag by the system.

if you picked your own gamertag when you first started the account then that was your free gamer tag pick.

so in your case you will need to pay for the gamer tag that you typed in yourself.

You can easily change your Xbox LIVE gamertag. If your gamertag was created for you during Xbox LIVE sign-up, you can change the gamertag once for free.

http://support.xbox.com/en-US/billing-and-subscriptions/account-management/change-xbox-live-gamertag

If this is a newly created account, you still get one free gamertag change. I'd take advantage of that while the offer is still available.