Hello Georgina
When it comes to account recovery/identity verification, the process is a bit rigid on purpose for security reasons and there's little anyone at support could do to help.
If you have the authenticator App set to your account and you don't have access any more to the device to authenticate, you have the option to recover your account credentials on your new device with the steps in the link however make sure you don't have a personal Microsoft account already set up in the authenticator app;
To get more help from the Microsoft account teams please use the chat link below and then you can request a call back. https://support.microsoft.com/home/contact
- Click on the link and in the search you could put in account issues
- Scroll down and you should see the option contact support or sign in to contact support
- you can sign in with a different email
- for product select microsoft 365 and office and category select manage profile information
- you should see the option Chat with a support agent in your web browser
- confirm your email and it should take you to a support agent where you can provide your number and request a call back on continue via chat.
Best regards,
Dimitri Redant