We read about the Serpent, the ancient enemy, in the Book of Genesis, then the sins of the people who had relationships with the Sons of God and the appraance of Nephilim on the earth then the wrath of God and the flood. After that we read about how God lead Abraham, Issac, Jacob and His decedents to the Chosen land, but before entering the chosen land we again hear about the Nephilim (Numbers 13:33). Other than this there is no explict call out of Satan or His demons till in 1 Chronicles 21:1 Satan rose up against Israel and incited David to take a census of Israel. Also, we read David praying Psalm 51:11 Do not cast me from your presence or take your Holy Spirit from me.
Though we dont see Satan or his demons being explictly called out, it does not mean that he was not working. We see that the people of Israel were sinning against God, one after another, they built the Golden Calf, they murmured and rebelled against God, which brought forth the wrath of God. The Israelites were given the law to follow, and sin offerings be made to God.
When we compare our Journey from Baptism to Heaven, we mostly talk about Holy Spirit, this does not mean that Satan or His demons have completly vanished from our lives. They are working in our lives and leading us to places and situations which are sinful in the eyes of God and brining in their influence over our minds, spirit and body cutting our relationship with God. Now, by repenting and claiming the sacrifice of the Lord on the cross we get delivered from our sins and break ourselves free from the clutches of the devil and his demons. Satan exists and is related to every sin, pain and suffering we have to hold on to the blood shed on the cross by our Lord Jesus Christ for our deliverance every day and put on our armor as we resist and grow stronger in the Lord.