He hardened his own heart. He may have been sincere during the crisis. Seeing the relief of such a curse is just as impressive as seeing the power of seeing the curse come about in the first place. What should have been convincing and convicting to him merely emboldens him further.
The same may be true in our own witnessing. A hardened heart is rarely convinced by rational conclusions. If signs and wonders are not enough, if the heart has given it's word and then turned on it, it now has much more than it's own image to rescue and maintain, it now must bend the situation developing by it's own will. His own magicians he must feel are weak and deserters, under the spell of others. Everyone else is wrong but him. Have you seen it?
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3