Does Black Magic Really Exist or its just in one's mind!

What is black magic? I heard that it’s a spell that can hurt someone even if you are a good person. Does it exist or not?

The past 3 weeks, I have strangers coming to me and warned me to be careful with those people around me. Just like yesterday, after I had lunch with my friend Sheila at Ampang Point, we stopped at this kiosk selling head scarfs. I am not the type of person who likes to wear fashionable headscarfs but just plain black. So I don't really bother to buy new ones. But yesterday, I dunno why but I just decided to stop and tried a few.
The sale person who is in her early 20s while putting on the headscarf for me, she suddenly said , "Kak boleh saya cakap sikit?(Sis, can I tell you something?)". I looked at her and said sure go ahead. Then she said " Kak hati-hati ya."(Sis, Please be careful yeah). I thought she was just telling me to be careful of pick pockets or snatch thief but then she continued."Ramai orang dengki dekat akak and sekarang guna ilmu hitam buat akak sakit and orang-orang ni takkan berhenti hingga akak hancur".(You have lots of people envy and at the moment are casting black magic spell against you and they will not stop until you are totally destroyed). So I told her, that me using the walking stick has nothing to do with black magic but due to my bone cancer. Then she told me that not about my walking stick but the bleeding i have been having since March.
I looked at her in silence and then she told me that she is from Sabah and that she has this ability to see. Maybe it's God's way of telling me to be careful because she is the 3rd person in 3 weeks.
1. As much as i know it exists but to me there is no power except Allah's, so I am not gonna be afraid and shall just pray to Him and redha. No way I am gonna see people so called "Orang Alim" 2. To me they can do what they want to do as long as I keep on forgiving them, I will not fall into the category of SHIRIK/ Kufr. Last week a client called just to tell me the same but only a little bit detail saying that this people are using Indonesian black magic. Why be afraid. Things happen only with HIS PERMISSION.
Black magic does exist and it was even performed on the Prophet of Allah (Allah bless him & give him peace).

‘A Jew by the name of Labid ibn Asim who outwardly posed to be a believer (Munafiq) carried out black magic on the Messenger of Allah (Allah bless him & give him peace). He took the hair of the Messenger of Allah (Allah bless him & give him peace) and made eleven knots and placed it under a rock in a well called Zarwan.

The effect of this was that it created uncertainty in the mind of the Messenger of Allah (Allah bless him & give him peace) as to whether he had done or not done certain things (although this had no effect on his religious and prophetic obligations)

At times the Messenger of Allah (Allah bless him & give him peace) felt he had accomplished something yet he had not done so and vice versa. The angel Jibra’il informed the Messenger of Allah (Allah bless him & give him peace) as to what had occurred and came down with the two Surahs, namely Surah al-Falaq and Surah an-Nas. The Messenger of Allah (Allah bless him & give him peace) together with the Companions (Allah be pleased with them all) went to the well and removed the knotted hair. As each verse was recited, the knots untied miraculously.

At the eleventh knot, the Messenger of Allah (Allah bless him & give him peace) was relieved from the effects of this black magic. [See: Tafsir Ibn Kathir & Ma’arif al-Qur’an]

'Sayyida A’isha (Allah be pleased with her) narrates:

“Whenever the Messenger of Allah (Allah bless him & give him peace) would become ill, he would recite the Mu’awwizat (Surah al-Falaq & Surah an-Nas) and blow over himself. When his illness was aggravated, I used to recite these two Surahs (and blow my breath) over him and make him rub his body with his own hand, for its blessings.” [Sahih al-Bukhari, no. 4728]

Also, the consuming of Ajwa dates has been prescribed by the Messenger of Allah (Allah bless him & give him peace) as a remedy for black magic. Amir ibn Sa’d narrates from his father that the Messenger of Allah (Allah bless him & give him peace) said:

‘“He who eats seven Ajwa dates every morning, will not be affected by poison or magic on the day he eats them.” [Sahih al-Bukhari, no. 5130]

May Allah forgive those who practice BLACK MAGIC and open their heart to the right path.