Hello, I am replying to the OP only.
You overlooked that the satan still had some access Heaven before Jesus was born. The story of Job tells us this. After the resurrection, all such access was cut off. The enemy was defeated at that point once and for all. Jesus claimed the keys to hell and he locked the enemy away for all times.
Demons are the enemies minions, fallen angels and perhaps other things as well. I have my own theories but it matters little.
Humans can hear both the Lord as well as the enemy. This is an internal connection that you can feel right this very moment. The enemy seeks to lead you from the Lord. He will use what you are most vulnerable to, sins of the flesh are a common tool but do not ignore the mental traps either! I think that is what you are doing here.
If you read only one thing I wrote let it be this: All you need to do is accept Christ. There is nothing else, at all that you need for salvation. If you honestly accept Christ the life that you live will be filled with opportunities to bear His light to the world. Be a bearer of light brother, ignore all the ways the enemy tries to make you doubt your own faith. Do not let the enemy humiliate you on the inside for your faith. He will constantly try to do this brother, be wary of it.