I would like to ask where do witchdoctors get their magic or ability to heal?
First, we have to consider whether witchdoctors actually have any power or abilities, such as to heal. Like the so-called faith healers and people who claim to be witches, there is no true evidence that any healing takes place. We don't have medical evidence that a person had a verified malady. Nor are we show evidence that after the so-called healing that they no longer have the malady. Typically these people claim to cure things that cannot be seen, such as headaches. Contrast this to Jesus curing a man with a withered hand (Mark 3:1-6). Or they will do things that are equivalent to a magic trick done by a magician. There is no real magic but a deception based on a sleight of hand.
This is what you would expect. Satan's power is lies (John 8:44). His followers are the same. "That is, the one whose coming is in accord with the activity of Satan, with all power and signs and false wonders, and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved" (II Thessalonians 2:9-10).
"The LORD is for me; I will not fear; What can man do to me?" (Psalms 118:6).