All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Black magic means using talismans, enigmas and mysteries to seek help of devils in order to effect the hearts and bodies of some persons.
This practice is among the major sins. Abu Hurayrah narrated that the Prophet said: “Avoid the seven great destructive sins”; they (the people) asked, “O Allah's Apostle! What are they?” He said, “To join partners in worship with Allah; to practice sorcery; to kill the life which Allah has forbidden except for a just cause; to consume Riba (usury); to consume the property of an orphan; to give one's back to the enemy and flee from the battlefield at the time of fighting; and to accuse chaste women who never even think of anything touching chastity and are good believers.”
No doubt, practicing magic is totally contrary to one's true faith in Islam, because this act consists of Shirk (associating partners to Allah) in many forms, such as worshipping Satan, seeking his help and refuge, etc.
Allah Says (what means): {And they followed [instead] what the devils had recited during the reign of Solomon. It was not Solomon who disbelieved, but the devils disbelieved, teaching people magic and that which was revealed to the two angels at Babylon, Harut and Marut. But the two angels do not teach anyone unless they say, “We are a trial, so do not disbelieve [by practicing magic].” And [yet] they learn from them that by which they cause separation between a man and his wife. But they do not harm anyone through it except by permission of Allah.} [Quran 2:102]
The best treatment for any magic is the recitation of the Quran and the authentic supplications taught by the Prophet Muhammad . In fact, the whole Quran is a remedy and a benefit for the one who believes in it. However, there are some Quranic portions, that have special qualities such as: Surah Al-Fatiha, Ayat al-Kursi (Quran 2:255), the last three Surahs of the Quran, and the last two verses of Surah al-Baqarah (2:285-286), etc.
It is also permissible for the one who is bewitched to ask a pious, religious person to recite upon him some verses of the Quran and authentic supplications; this is what is called Ruqyah.
But going to fortune-tellers or magicians is forbidden. The Prophet said: “The person who goes to a fortune-teller and believes in his sayings has disbelieved in what was revealed to Muhammad.” [Ahmad]
Therefore, using talismans or amulets given by magicians or fortune-tellers is forbidden.
To conclude, the existence of black magic is a fact and practicing it is Kufr (disbelief). Whoever seeks help from the devils while practicing magic is a disbeliever according to the consensus of the Muslim scholars. And whoever claims that practicing it is permissible, is mistaken.
Allah knows best.