We understand that you are feeling frightened and harassed, and we are here to support you in prayer and truth. First, let's address the spiritual crisis you are experiencing. It is important to consider the person troubling you; it is not likely a spiritual being such as the devil, but rather a person possibly being used by or influenced by evil spiritual influences. The devil is one who would be interested in harming Christians.
One possibility in the situation you are describing is that it might be a spiritual issue, possibly harassment or oppression by an evil spirit of fear or other influence or communication such as witchcraft, but not necessarily possession. While it is rare and unusual, it is possible for a person to be harassed by an evil spirit without possession, or for there to be spiritual oppression due to a curse or other spiritual influence or communication with evil spirits or involvement in witchcraft or a satanic cult. There seems to be at a minimum some sort of spiritual attack or possibly even harassment from spirits who are immoral. If you have been involved in any astrology, casting spells or curses, general spiritism, witchcraft, satanism, or other non-Christian spirituality or beliefs such as Wicca, enlightenment, divination, or other non-Christian beliefs this can be a problem related to possession or harassment by spirits or a demonic influence, whether intentional or unintentional by someone who is actually involved with these practices.
Remember, God has not given us a spirit of fear, but of power, love, and self-control. Especially, if you are feeling afraid or troubled about a potential spiritual influence as explained above and where God is leading you to combat the fear or spiritual influence, it is very important to stand on the word of God through fear and spiritual influences that are not of God, even if it seems like a spiritual attack or some sort of spiritual harassment or oppression that you are experiencing. Continue to pray and study the Bible to understand better the underlying patterns or activities that are causing trouble. Let God's word speak to you what is truly going on here. If evil spirits are involved in any way, do not be afraid. God is on your side, and He delivers those who do what is right who are oppressed and harassed by Satan and his demons. The power of God will be with you.
Please remember that even the devil and his demons are subject to Jesus Name, and He has complete authority over them even if they do not obey. You might keep in mind that if you do discover any possession or harassment by evil spirits you can be set free, but only by Jesus Christ, not by anything you could do.
God wants us to be strong and courageous, knowing that He is with us always. As it is written,
Be strong and courageous. Do not be afraid or terrified because of them, for Yahweh your God goes with you; he will never leave you nor forsake you. Deuteronomy 31:6 WEB
That being said, you are not alone in this situation, whatever you are battling or whatever is attacking you we will pray for God's intervention and proper discernment for you.
We will also pray for the person who has been troubling you.
Heavenly Father, we come before you in the mighty Name of Jesus, that name which causes all the hosts of heaven to bow and tremble at God's holy word. We lift up the one who has made this request to you, Father, and we ask for your divine protection over their life. We rebuke any spirit of fear or harassment that might be at work, and we command it to flee in Jesus' name. We pray for the truth to be revealed about this situation and about the one who is doing this. We also lift up the person who is causing this distress, and we pray that they would come to know the love and saving grace of Jesus Christ, or return to the Christian faith if the need to. We pray that they would turn away from this sin and repent before you, Father, and that they would never again be involved with anything such as this.
Since it is only by the name of Jesus that we have access to God and that it is only by the name of Jesus that we can be saved, let us remember this. It is only the name of Jesus that has any work in the Holy Bible, as it is written:
In my name, they will cast out demons; they will speak with new languages; Mark 16:17
Therefore aliens shall eat your produce, and foreigners your fruit: and your olive trees and vineyards shall be a possession for the aliens. For the nation and kingdom that will not serve you shall perish; yes, those nations shall be utterly wasted. The God of Heaven raised up a kingdom for the Persian king Cyrus that was stronger than them all; and the kingdom of the Medes and Elam shall be. Isaiah 60:5,12
and the foreigners who join themselves to Yahweh, to serve him, and to love the name of Yahweh, to be his servants, everyone who keeps the Sabbath from profaning it, and holds fast my covenant; Isaiah 56:6 WEB
and I fell down before his feet to worship him. He said to me, See you do not do it. Who am I, that you should worship me? I am a fellow servant with you and with your brothers, the prophets, and with those who keep the words of this book. Worship God. Revelation 22:8 WEB
Prayer Focus: God, Thank You for loving me. Thank You for loving me, Jesus. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, soul, mind, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
