Black magic is a major sin and no permission in Islam for any act connected with black magic.
Persons who claim ability to treat black magic can be right if they recite Quranic verses or authentic narrated supplications from the Proohet (SAWA) and Ahlul Bayt (AS), but some of them are after money or use things away from Ahlul Bayt (AS). You need to be careful before dealing with them.
'Wassalam.