Exorcism 

You can fool a human into saying you're a devoted Christian, but you cannot fool Satan, as a demon feeds on the sins in the heart. In Acts 19:13-17 we see how a group of men attempting to preform exorcism too. The evil spirits give recognition of Jesus. Of Paul. But not of them. 

And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye?

The possessed man attacks the group of men: and the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded. And this was known to all the Jews and Greeks also dwelling at Ephesus; and fear fell on them all, and the name of the Lord Jesus was magnified.

An Unclean Spirit Returns (Matthew 12:44 (Luke 11:24-26))

When an unclean spirit comes out of a man, it passes through arid places seeking rest and does not find it. Then it says, 'I will return to the house I left.' On its arrival, it finds the house vacant, swept clean, empty and put in order. Then it goes and brings with it seven other spirits more wicked than itself, and they go in and dwell there; and the final plight of that man is worse than the first. How can this be? 

A person who commits sin without repenting does not have the protective influence of the Holy Ghost. Therefore, an evil spirit enters and dwells therein, thus leaving him "unto himself."

Exorcism Procedure

You got a problem? You talk to God.
Jesus himself said, "After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name "(Matt 6:9). 1 Peter 5:7 Give all your worries and cares to God, for he cares about you
Matthew 7:7 Ask and it will be given to you; seek and you will find; knock and the door will be opened to you

Matt 18:20 For where two or three are gathered together in my name, there am I in the midst of them. 

Again I tell you, you can fool a human into saying you're a devoted Christian, but you cannot fool Satan, as a demon feeds on the sins in the heart. A house that was supposedly cleaned decades ago by a priest was not cleaned at all. Evil was still present and was only driven away when a saint arrived and prayed to the Father directly. Priests at least from the Catholic church as I am aware of pray to Mary. You do not want to please the demon so he stays put. You do not pray to anyone else than the Father. And the Father is a jealous God. He would not want pictures (etc) of another 'god' in your house. Clean your house (residence, mind and soul). 

Demonic possession

Demons do not have physical bodies like humans and animals

Therefore they are eager to take over or destroy a body with vices. 

In 2008 in the UK, the muslim Mohammed Boudjenane decapitated his neighbour and carried the head in a bag onto a bus.

Before doing so, he raped and beaten a Christian woman several times, shaved her head and told her she would only be released if she would convert to islam and marry him.

He said he could not remember any of this, was suicidal and claimed to have heard voices in his head.  

In 2008, immigrant Vince Weiguang Li numerously stabbed, decapitated and ate the flesh of a fellow passenger aboard a bus in Canada. Li's employer said in an interview that Li was one of his most reliable carriers; "He was very punctual and always cleanly dressed. He was a very nice, polite guy. We would've had no reason to let him go before all this happened." When Li was asked in court if he wanted a lawyer, he softly said "kill me please". He claimed to have heard 'God's voice'.

In the Netherlands in 2007, a Chinese homosexual immigrant only known by initials, had cut a young man to pieces with an axe and chainsaw, stripped the flesh of the bones, deep fried, wokked and cooked the flesh. He claimed to have done so because 'his Gods were angry at the boys Gods'. After the murder he decapitated a bird because he believed there was an evil spirit in the bird. Ted Bundy as well as the Son of Sam both claimed they were driven by a demonic entity to commit their crimes.

Calling upon demons

Witchcraft (fortune telling, runes, tarot, druids, charmers, mediums, clairvoyance etcetera) was practiced in ancient Sumeria, Babylonia and Egypt, among many other countries such as Greece. Various sources state that (fallen)angels from the sky had given powers, certain knowledge to the humans in the time of Sumeria. The Jewish kabala, and Wicca, being one of many. The difference between God and the devil is that God's prophecies are always 100% accurate, not 50%, not 25% or 75%.

Hosea 4:12-13 My people ask counsel at their stocks, and their staff declareth unto them: for the spirit of whoredoms hath caused them to err, and they have gone a whoring from under their God. They sacrifice upon the tops of the mountains, and burn incense upon the hills, under oaks and poplars and elms, because the shadow thereof is good: therefore your daughters shall commit whoredom, and your spouses shall commit adultery.

Rev 21:8 ..the fearful, and unbelieving, the abominable, murderers, whoremongers, sorcerers, idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.  

To whom hell awaits after Judgement Day

Matthew 8:28-29 And when he was come to the other side into the country of the Gergesenes, there met him two possessed with devils, coming out of the tombs, exceeding fierce, so that no man might pass by that way. And, behold, they cried out, saying,

What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?

Matthew 25:46 And these shall go away into everlasting punishment: but the righteous into life eternal.
Matthew 13:50 And shall cast them into the furnace of fire: there shall be wailing and gnashing of teeth.
Mark 9:48 Where their worm dieth not, and the fire is not quenched.

Beware of the Sharks 

This reminds me of a lagoon in French Polynesia (source of this perfectly explained shark story). It is one of the largest lagoons of its kind in the world. It is of beautiful turquoise color because of its white sandy floor. The water level lowers and rises ever so slightly with the ebb and flow of the ocean tides. The lagoon is peaceful and calm, but the pass through which the tides rush is treacherous and filled with sharks that await an easy meal. One day a few tourists swam too close to the pass and began to be dragged toward danger. The peacefulness of the lagoon had led them to be careless and lazy in keeping themselves from the sharks. Gradually they had floated on the soft current toward the pass. Eventually they went too far and found themselves beyond the point where their own abilities could save them. Outside help was necessary, so a speedboat was sent to rescue them. As the swimmers in this lagoon should have done, we need to put forth a consistent, positive effort every day in order to remain in safe waters. We need to develop good habits that can replace old, bad ones. Satan desires that we become lazy and complacent. Daily scripture study and prayer, service, repentance, and following the promptings of the Holy Ghost can keep us safely in the spiritual waters of the Lord.