I believe you. My own daughter had a similar experience.
Scientists refuse to believe there is a spiritual dimension, but that is because the refuse to believe God is real, so they have to explain everything by filtering and twisting evidence to make it fit their beliefs.
But there are millions of people who have experienced the spiritual dimension. There are demons, and there are angels. Satan is real, and so is God. Each person has a soul that does not die, only the body dies.
The shadow you saw was definitely evil. Black is the color of unrighteousness and darkness.
Jesus Christ is light, and all the redeemed wear white robes. Angels are white and brilliant. Demons and evil spirits are black figures.
How did he get there? There is something in the house that gave him the keys. If anyone brought anything that God called cursed into the house, that will do it. Or if someone watched horror movies, vampire movies, zombie movies or anything like that - that also gives them a legal right to come inside.
How do you get rid of it?
The only name in the universe that makes them flee is the name of Jesus Christ, and the Word of God.
That is why it is so important to make sure Christ is living inside of you.
Imagine you die in a car accident, your soul leaves your body, and 30 such evil spirits come after you and you have no protection? Jesus Christ is your only protection.
Make sure you receive him as your Savior and play Christian worship music on your phone (Terry Macalmon, Acoustic worship, Julie True or something like that). They can stand it because worship music attracts the presence of the Lord.
How to accept Jesus Christ as your personal Savior and Lord?
It is the easiest thing in the world. Just close your eyes, focus on him and pray something like this:
"Lord Jesus, I repent of all my sins and I ask you to wash me clean. I am sorry for all the bad things I have done and the many times I broke God's Will. Please forgive me and fill me with the gift of the Holy Spirit. I want to belong to God. I want to be adopted into his family as his child. Come into my heart. I give you control over my life. Please lead me through the Holy Spirit and make your Word real to me. Fill my soul with the peace that surpasses understanding and help me change so that I may lead a life that is pleasing to you. I want to go to heaven and I want to be called by the Fathers name. As of today I declare that I belong to you". Amen
If you do this with all of your heart you will start noticing subtle changes inside of you and step by step your life will change. I am speaking from experience.