Thank you for posting your question in the Microsoft Q&A forum.
Based on the information provided, it appears you are unable to complete the sign-in process, as the device registered for multi-factor authentication (MFA) is no longer accessible to you.
To provide you with the most relevant support, I first want to understand your account type, as the handling process is different for each. Could you please answer the following questions?
- Is your account a personal Microsoft account (such as Outlook.com, hotmail.com) or a work or school account provided by your organization (like yourorganization.com)?
- If your account is a work/school account, are you an end-user, or are you the (or one of the) IT administrators for your organization?
Once I have that information, I can assist you more effectively. Please feel free to reach out if you have any further questions or concerns.
Note: Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.
I'm looking forward to your reply.