Sign up with email/password after Signing up with Social Account

Hi there - A good number of our users use Social Sign up. We recently had someone (Person A) access another user’s account (Person B) by “Signing Up with Email” using the same email as someone who had already signed up using Social Sign up. Person A was basically able to Create a New account with the (Email/Password option) and login into Person B’s existing account. How do I prevent this from happening?