Firebase, Auth with phone & google

In my application I use Firebase to authenticate myself.

First the user is authenticated with the phone, I need to verify it, and then at the time you want, you can log in with google to have a better experience on the app...

The login in both makes it perfect, I have no problem with that, it's more, you uninstall the app, reinstall it and it's as if nothing had happened.

But the problem I have is that when the user changes his phone number and re-enters the application (eg: uninstall and reinstall) is registered with his number, then if you want to use your google account, I get this error:

SIGN_IN

com.google.firebase.auth.FirebaseAuthUserCollisionException: This credential is already associated with a different user account.

REAUTHENTICATE

com.google.firebase.auth.FirebaseAuthInvalidCredentialsException: The supplied credentials do not correspond to the previously signed in user.

Which is what I can do so that the user can reuse his google account with another phone until now I come erasing the old users, but it is not good that.

Or what other alternative do I have?

PS: if they say to activate multiple accounts by mail, it does not work...

from Firebase, Auth with phone & google