I had a c&p scheduled for me also. I callled my VSO, and she wrote a letter to the VA. The letter stated that since I was p&t for PTSD, I should not have another exam. The VSO told the VA to cancel the exam.
My situation might be a little different. Originally , I had asked for an increase of my PTSD rating from 70 to 100. I decided to withdraw my claim for an increased rating, but the VA wouldn’t cancel the exam.