The existence of Sihr and Jinn are very indeed real and they have been mentioned in the Quran. An entire chapter is named after the Jinn (Surat Al Jinn).
“And the jinn We created before from scorching fire”.
It is also mentioned in Surah Rahman, verse 15 :
“And He created the jinn from a smokeless flame of fire”.
So the existence of Jinn is definitely real as the Quran tells us that they exist but they belong to the world of the unseen. Interaction with jinn is very rare as they only are communicated with through magic. Many cases however, you can experience such an occurrence if a jinn falls in love with you, or a magician linked you to one, or you accidentally or intentionally harmed one. That's why it's required for safe measurements to say Bismillah when throwing hot water into the sink or bathroom or jumping from high places, etc. Jinns have free will just like us, unlike the angels who don't. So they can choose to be good or bad. The evil ones amongst them are the shayateen who follow after their leader Shaytan (Iblis) So they are the plural of his name. The good ones are just jinnis who can be Muslim, Christian, Atheist, Hindu, etc.
Now onto the black magic part,
Magic is also mentioned in the quran. Two angels by the name of Harut and Marut were the ones who introduced magic during the time of the Prophet Sulayman (Solomon) alayahislama.
They followed what the Shayāṭīn (Satans) gave out, in the Mulki Sulaymān (مُلْكِ سُلَيْمَان, Kingdom of Solomon). Sulaymān did not disbelieve, but the Shayāṭīn disbelieved, teaching men magic and such things that came down upon al-Malakayn bi-Bābil (ٱلْمَلَكَيْن بِبَابِل, the Two Angels in Babylon), Hārūt and Mārūt, but neither of these two taught anyone, till they had said, "We are only a Fitnah (trial), so do not disbelieve." And from these, people learn that by which they cause separation between a man and his wife, but they could not thus harm anyone except by the Leave of Allāh. And they learn that which harms them and profits them not. And indeed they knew that the buyers of it (magic) would have no share in the Ākhirah (Hereafter). And how bad indeed was that for which they sold their own selves, if they but knew!
'I seek refuge in the Lord of daybreak. From the evil of that which He created. And from the evil of darkness when it settles. And from the evil of the blowers in knots. And from the evil of an envier when he envies.'" [Quran 113:1-5]
These verses specifically highlight the existence of sihr (black magic) because in the Quran, Surat al Falaq refers to protection from the magicians who blow magic and tie the magic into knots so that way it cannot be easily removed. That's why we recite this surah when we're trying to untie something difficult or to even remove magic. There are many videos in how the magic works and how magicians call upon the jinn to help them with magic. There are also Muslims who have documented their experiences with sihr on youtube if you want to give it a try. I've never deal with these situations personally but I know many people who have. May Allah swt have mercy on us and may He protect us from the evil of the devil and all of mankind allahuma ameen. If you have any more questions, don't hesitate to contact me back! Jazakallah khairen