Merge account that is associated with a gamertag?

There is no way to merge accounts. You can try contacting support and as long as you can verify that you are the owner of the account, they should be able to get you the email. 1-800-4my-xbox if you're in the US/Canada or
support.xbox.com/contact-us

Hello, sorry no way to switch or merge your gamertags. Only option you would have is changing the mail email address associated with the account.

Hey mate, I'm having a little trouble understanding. Do you want to merge two accounts together or are you trying to change the MS account (email) associated with the gamertag that has gold?

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If you want to merge the accounts together, that unfortunately is not possible.

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If you're looking to change the email please take a look at the steps here:
support.xbox.com/.../switch-gamertag-to-different-microsoft-account

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If for some reason you logged-on to xbox.com with the Microsoft account that isn't associated with a gamertag it would have created a random one which is why you're getting that error.

If you are getting that error, it means you can't merge the two accounts. It's possible that another gamertag or billing account is associated with the account that you are trying to move the gamertag over to. In general, I'd recommend adding an alias to
the account instead of changing MSA anyway. (See previous post)

Did you speak to Customer Support about your account? If not, please do so.

Gamertags or accounts can't be merged. And the save games are still there but associated with the old Gamertag. So the best thing to do is getting your account back. Please call Xbox Support of your region.