Hello @欣 陈
Thank you for posting your query on Microsoft Q&A.
Based on your description, it appears that you are unable to log into the Azure Portal due to MFA deletion. Since the device registered for second-factor authentication are not getting any MFA prompts, you are unable to complete the authentication.
In such scenarios, another Global Administrator can help to re-register MFA on a new mobile device. However, since you mentioned that you are the only Global Admin in the tenant, this qualifies as a tenant lockout scenario. To resolve this, we need to engage the Data Protection team via a support ticket to unblock your access.
To proceed, I will need a few details from you. As this information contains Personally Identifiable Information (PII), please share the following details via private message:
Contact phone number (add +Country code)
Contact email address
Global admin email address (affected account)
Country
TimeZone
Please send me the detail via private message.
We can then connect offline to discuss further and assist you in resolving this issue.