Can't prevent same phone number on MFA with SMS


Now, I’m creating a web app that has some connections(Twitter, Facebook, id and password, …etc).

I want to prevent one person from illegally creating some SNS accounts with same phone number.
For example,
・you can create 20 google accounts, link them to same phone number.
・you can create google account and facebook account, link them to same phone number.

I would like to use MFA with SMS authentication so that only one account can be linked to one phone number.

What should I do?

Thank you for your help!