1. The spiritual world is legalistic. There are rules just like there are laws in our world. God wrote the laws and God enforces them.
2. Usually we break the rules and through our free will allow evil spirits to start affecting us. When it is simply allowed by God it is usually to encourage our spiritual growth or show us the reality of the spiritual world. In the midst of things it's hard to see this but usually after a short period of problems a lifetime of spiritual growth follows.
3. Spiritual "legal rights" can be given to evil spirits, people, buildings, objects, or family lines.
Possession is the most famous example, being full rights to the body of a person and therefore ability to take over their body. Rights of that level are almost always explicitly given by the person, usually in exchange for something. Rights to oppress a person are usually given by spirit communication, the occult, or black magic.
Rights to a building are usually given through the rule breaking that goes on there, or through explicit permission from the person with authority over the building. When we bless a home with the owners request we mark that territory for God, the opposite happens with black magic and serious violations of God's rules. Rights to a building usually leads to infestation by evil spirits. Once they are in through free will they have to be cast out and then the home has to be claimed for God.
Rights to an object is a common way that people involved in black magic get spirits into a persons home or life. They cast "spells" on an object that give rights to evil spirits to attach to it. Then they try to get the target to accept the item as a gift, etc. Then through free will the person has brought a spirit into their life. Sometimes they simply break in and leave the object hidden in a home, sometimes they leave it behind after a visit.
Rights to a family line are usually given in multi-generational cults that serve evil spirits. Usually these spirits try very hard to stay with the family once they are in, often afflicting the next generation starting a few years before their current host will likely die.
4. Spiritual rights to a person can be limited, taking the form of having spirits in them, but not having them take over their body. This generally takes the form of spirits residing in the body, felt by the person at times and felt violently during prayer over them. This requires the Sacramental life and deliverance work, not an exorcism. It is not uncommon for people with spirits in them to have untreatable medical conditions that stop as soon as the spirit is cast out.
5. There is often a mental health component to situations with spiritual affliction. It is normal to be frustrated and possibly depressed after being harassed by spirits for some time. It's also not uncommon for spirits to cause physical health problems if they are inside of a person.
6. Once rights are obtained by evil spirits they do not give them up without being forced to. They may make it seem like they will but it's a lie. The rights must be renounced and then prayer must be said to cast out/away the spirit. Prayers to fill the space occupied by the evil spirits with the Holy Spirit should follow. This could take the form of a baptism in the Holy Spirit, a house blessing, etc.
7. The breaking of rights and casting out/away of evil spirits is generally referred to as "spiritual warfare" or deliverance work. Deliverance prayers should only be used by someone trained and approved to do so. Catholic laity are not to pray "over" (or lay hands on) another person, they can pray for that person only. There are exceptions to this when someone has been deemed to have a charism for deliverance work and has permission. A special ritual within the Catholic Church, called exorcism, is done by priests with the permission of their Bishop for cases of full possession only.
8. Assuming that you are Christian or Catholic your first contact should be your local pastor or minister. You may find that you cannot find someone willing to work with you to determine if a spiritual problem is present and pray against it. If that is the case you may need to reach out to your Bishop's office directly.
9. There are cases that are simply mental illness that are mistaken for spiritual problems. Unfortunately serious mental illness can cause a state where a person is convinced they are possessed or that the voices they are hearing are spirits. It takes experience and evaluation by someone trained in mental health to identify these cases. It is imperative that medical and psychiatric situations not go untreated because the spiritual hypothesis has been accepted inappropriately.
10. Many Christian and Catholic parishes have prayer meetings or people that pray deliverance prayers. There are many people who call themselves demonologists or exorcists. It is important to verify that they have been trained and have a calling to this work, usually through their church (Bishop's office).