Unfortunately, it’s not possible to avoid the user being created when attempting to login with social connections.
One workaround might be to use an Auth0 Action to deny them access using the api.access.deny() method.
Alternatively, you could use the Action to log the user out to clear their session and then redirect them back to the login page.
api.redirect.sendUserTo('https://TENANT_DOMAIN/v2/logout', {
query: { returnTo: 'WHITELISTED_LOGOUT_URL' }
Thanks,
Rueben