Demons exist. To do a deep study of demonology you would need to understand the Hebrew Qliphot, the Tree of Death where there are 10 corresponding Infernal Abodes versus the Tree of Life where there are 10 "Heavens".
In the Tree of Life we have 10 Archangels, each ruling their own sphere.
In the Tree of Death we have 10 Archdemons (Fallen angels) ruling each of the hells.
In the book "The Lesser Keys of Solomon" he worked with 72 of these demonic entities, recording their position, their sigils, their functions and skills, and he used them to help build the Temple of Solomon.
There are limits to what demons and angels can do. In this plane of existence, they do nothing unless we approach them in the correct way and ask for help or for something we need them to do. And then we have to approach them in the correct way as well.
This goes for both angels and demons.
All of this work depends on YOU being SOUL aware or SELF aware. (KNOW THY SELF)
Most people on earth are unfortunately NOT SOUL AWARE and then we risk being the playthings of the demons, who view us a disgusting ignorant pathetic meat suits practicing worthless religions.
So - to remedy the situation: BECOME SOUL AWARE.
This is a meditative process whereby you need to become aware of the fact that you are a Divine SOUL. You are NOT lost as a poor sinner. You are simply asleep and need to awaken. You are already eternal and have eternal life.
God split himself up into billions of fragments, divine sparks, which became the souls now inside of us. You are I are all God having a human experience. We chose our path, our life in this realm, and all is here helping us to awaken. Some have already awakened, but most of us are still asleep.
There are some guided meditations you can find on Youtube, for the purpose of Soul Awakening.
https://www.youtube.com/watch?v=v6wRAUThbIU
Soul Awakening is the process of entering the Kingdom of God.
Once you know WHO you are the concept of sin and church and religion will become irrelevant to you, as it did to me.
Also, you will understand that YOU are God knowing that God is in you , and the demons will not bother you - Greater is he that is in me, than he that is in the world.
You will learn to take responsibility for your life and choices, and not blame demons or others for making bad choices or sinning etc.
You will build a strong relationship with your SOUL, learn how to receive messages and communicate with the SOUL / Divine within.
Blessings on your journey.