My gamertag was changed and then taken by another account

Hello McKenzie Z, My name is David. I am an independent advisor, happy to help you today.

I'm sorry to hear that you've had problems with your gamertag on Xbox Live. If your ex-partner has logged into your account, she has changed your gamertag, and created a new account with that gamertag, here are some suggestions on what you can do:

Change your password: The first thing you should do is change your Xbox Live account password to make sure your ex-partner can't access your account again. This will prevent you from making additional changes.

Contact Xbox Live Support: Contact Xbox Live Support immediately to inform them of the situation. Explain in detail what has happened, including your ex's action of changing your gamertag and creating a new account with it. Provide as much relevant information as you can, such as the email associated with your account and any proof of ownership you may have.

Provide proof of ownership: If you have proof of ownership of your account, such as receipts from previous purchases or any other information that shows that the account belongs to you, be sure to provide it to Xbox Live Support. This can help verify your identity as the rightful owner of the account and support your request to revert the gamertag change.
https://support.xbox.com/help/account-profile/profile/change-xbox-live-gamertag

Follow the instructions from Xbox Live Support: Xbox Live Support will guide you through the process necessary to resolve the issue. Follow their instructions and provide them with any additional information they ask for. Please note that the process may take time and you may need to be patient as you work with support to resolve the issue.

Remember that Xbox Live support is the appropriate entity to help you in this type of situation. They have the necessary resources and authority to investigate and take appropriate action. I hope you can solve the problem and get your original gamertag back.

Best regards.

My Microsoft account now has a gamertag of xyz when it use to be "andy". If I try and change to andy I get the message "andy is taken. Please try another."

Already taken as Gamertag: B Lights. The system doesn't count spaces or capitals.

It can be used by a Zune subscriber, Bungie.net account holder, banned or in limbo (i.e. original XBOX account that has not been converted over to XBOX 360). It can be associated with an account in another country. Or the user's profile who owns that account
is configured to prevent any public view via xbox.com or other sites (zune, bungie, etc).

google "blights gamertag"

It's simply not available.

Here's a bit on GTs from
our guide:

I can't change my Gamertag (GT).

Just because you can't friend request a GT doesn't mean it is available. First of all, all GT are tied to services like Zune or Games for Windows LIVE. If a GT doesn't exist on Xbox, it might be in use on one of those services. Also, spaces and capitalization
are not considered when looking for available GTs. For example, "Major Nelson" is the same as "MajorNelson" is the same as "MaJoR nElSoN". Basically if the service says the GT isn't available, it isn't available.

I heard old GTs are being re-added. When will "This GT" be available?

There is no schedule or estimated dates for when certain GTs will become available again. GTs are not an on-demand service. They will be available when they are available.