Managing personal Outlook.com account settings, security, and privacy
Hey there, Sophie L
Unfortunately, the only way to recover the Microsoft account is through the Microsoft account recovery form. Microsoft support have no insight into the recovery form and can't influence the decision.
I know this will be frustrating, because you need to get into your Microsoft account, but unfortunately what the support agent had told you is correct. In order to recover the account, you must submit an account recovery form for it to be reviewed.
Because Microsoft takes account security seriously, unless they are 100% certain you are the account owner, they won't reset your password or security information. In addition to this, if you have enabled two-factor authentication, they are unable to bypass this and reset it due to how the system works.
I am sorry I can't bring better news about this situation, but do hope they are able to help reset your account information.
Hope this helps,
Nathan