Not able to logon office 365 account or change it

Hello PeterHer007,

Are you the only IT Global Admin, if not then escalate your request to a Global Administrator ? 

The Global Administrator needs to follow these steps:

1. Log in to the Microsoft 365 Admin Center at https://admin.microsoft.com.
2. In the left-hand navigation pane, go to Users > Active users.
3. Find your account in the list and click on it.
4. In the user details pane, click on Manage multi-factor authentication. This will open a new window.
5. In the new window, find your name, and under the Multi-factor auth status column, you will see a link to Disable or Enforce.
6. Even if it says Disabled, the administrator should find the option to manage user settings or reset authentication options. They should select this to wipe your current MFA settings.
7. After the reset, the next time you log in, you will be prompted to set up a new MFA method from scratch, allowing you to register a new phone number or an authenticator app.

If you are the the only Global Administrator, you need to contact Microsoft support directly by calling them.

Hi, over here with similar issue. Replaced my phone last month, and needed to access the admin center

I'm the only admin, as I'm building a company IT Infrastructure

It there any contact we can have to address this issues?

Are you the only admin under your O365 tenant? Please try the below:

• Use Microsoft Authenticator App Instead of SMS
  If SMS verification is blocked, switching to the Microsoft Authenticator app may bypass the issue. You’ll need to set this up from a device that’s already signed in or through your IT admin.
• Ask Your Admin to Unblock MFA in Entra ID
  If you’re the admin, or can contact one, go to entra.microsoft.com → Protection → Multifactor authentication → Block/unblock users. From there, the blocked phone number can be reviewed and unblocked with a business justification.
• Register a Different Phone Number
  If possible, try adding a new phone number to your account via the Microsoft 365 Admin Center. This may require admin access or support from your IT team.