Won't pay, even after granting pre Authorisation.

My Son has a squint eye and I had to have a specialist see him. I followed procedure by taking him to the GP and got a referral letter. I then proceeded to call Carecross to find out which specialist I can take him to and they confirmed that there was only one in Gauteng and then they gave me the details of the specialist. I called the specialist and made an appointment. I called Carecross for an authorisation number, but the lady informed me that this specialist was not covered by them. I asked them why they had given me the specialist's details then and she told me she wasn't sure and will follow up and get back to me. She spoke to someone next to her and then informed me that she will grant the pre authorisation and proceeded to give me a reference number. My son's appointment was October 18th. They still refuse to pay even though they gave me the pre authorisation number, but cannot give me an answer as to why they won't pay. If they hadn't granted the pre authorisation, I would not have taken my son to the appointment.