Re: Black Magic.
Yes, black magic exists. It’s written all over the Qur’an. Black magic is performed by contacting a jinn and creating a contract, you are basically selling your soul to them in return for their services. At that point, since jinn are incapable of lying, they will carry out your orders until completed. Ever heard of the term ‘blood magic’? It’s the same thing.
I can’t confirm this through the Qur’an though but I have heard from several knowledgable people that black magic must be passed down to someone else before you die.
To answer your other question, yes there are people you can contact that can find out and they can even tell you who performed the act in the first place. Ask your local imam.