Momentum refuse to pay for MRI for accident injury

My son is still financially dependent on us. He is no longer a student, but we still pay monthly for his own medical aid at momentum. He played in a golf tournament in the Cape last year and was involved in an accident and sustained a bad knee injury and patella moved. At the ER they did x-rays. The orthopedic surgeon said that the knee is badly swollen and the swelling needs to go down in order to make a proper diagnoses. He said that he needs to see another orthopedic surgeon once back in Gauteng and gave my son a letter. Once back, he made an appointment with the recommended orthopedic surgeon, because my son is a professional golf player.Most of the orthopedic surgeons was on a medical conference at that stage and he had to wait almost 3 weeks to get an appointment. Before my son's appointment, he suffered major pain in the knee and went to the hospital where they removed the bandages. Again the orthopedic dr advised that the knee was swollen and they could not do anything for him at that stage. When he saw the orthopedic surgeon 3 weeks after the injury, the doctor did a MRI scan which is the only way to determine torn ligaments. Momentum is now refusing to pay for the MRI.