I second Dr. Adnan rana. The existence of kala jadoo could not be challenged. Its practice, as prohibited in Islam, is a subject matter of another discussion.

It was the knowledge of kala jadu, with the help of which, the birth of Hazrat Musa (A.S) was predicted, even before his arrival to this world.

Further, the last three Surahs of 30th para were revealed to help Hazrat Mohammed (S.A.W.S) counter the evil effects of kala jadoo upon him.