If the demons know that only one God exists?

Demons believe there is one God because they once lived in heaven before they were kicked out. They were once part of God's spiritual family in heaven. They shudder because they know how powerful God is and that God will soon use his powers to destroy them. But while they still have time, they are going to take down as many humans with them. This is why they continue to deceive people into believing that their is one true God but many ways to worship him which is so far from the truth.