issues with Astral projection beings

I don't know much about psychic readings of the mind or if it's possible through Astral realms since I didn't really believe in any of this... I know some people who I'm positive may practice this or some type of synching in the Astral realm, people with negative intent and who do it without permission....
I've been seeing a psychiatrist bc I was hearing demons and had actually seen a physical light human looking thing, anyway I know nothing of this realm and how to block people who do this... I'd like help with this bc it's strained my mental capacity to function and think clearly.