Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello. Jo Grady1
Thank you for posting in the Microsoft Community.
It appears that your username has been compromised and some scammers are constantly trying to send login requests to steal your account information.
Luckily, because your account has a login verification method added to it, which is the verification method you received with the CAPTCHA.
To better secure your account, I recommend that you add a new alias to your Microsoft account, set the new alias as the primary alias, and then unlink the email address associated with the originally compromised username.
Adding a new alias actually adds a new email address to your Microsoft account that you can use to log into your Microsoft account. Rest assured that this is just one more way to sign in, and the account you sign in to will still be the same Microsoft account you use.
Please click https://go.microsoft.com/fwlink/p/?linkid=864833 to add an alias.
For more information, please refer to :Add or remove an email alias in Outlook.com - Microsoft Support.
I hope the above information is helpful, if you have any questions or need further assistance, please feel free to contact me.
With best regards
InaX-MSFT | Microsoft Community Support Specialist