Managing personal Outlook.com account settings, security, and privacy
Since you are not aware of any 25-character codes, this means that you didn't enable the two-factor authentication (2FA) feature in your account.
However in this case, your only option to recover your account is through the account recovery webform.
Please follow this workaround to recover your account and to update your account's security info (landline number):
account.microsoft.com > click "Forgot Password" > select "I don't have any of these" > then you will be redirected to the ACSR form.
Providing as much information as possible will increase the chances of being verified through the automated process.
If your recovery request is successful, you will be asked to wait 30 days in order to update your security info and recover your account.
During this time, you will not be able to sign in to sites or services with your account.
You may check these guidance notes on how to fill out the form through this link: https://support.microsoft.com/account-billing/guidance-notes-for-the-microsoft-account-recovery-form-4dd8fef1-33d2-4fbe-9352-66127ab9b50e
In case you didn't receive the results from the account recovery webform, please try submitting another request via Incognito/InPrivate window and using different devices and network services. Then please check your email inbox, junk, and spam folders.
Please be advised that Microsoft Support will not be able to assist you with manual recovery, unblock, and escalation for this case, as stated in this article, that they are not permitted to send password resets, access, or even change any details on the account:
Best regards,
Darhyl