Customer Service out the door

I book at flight for my boss on FlyAfrica. It was a very good price. He gets on the plane this morning to realise that he is to tall for the seat he has been given and he is not even 6foot. Luckily the air hostess let him sit in one of the emergency exit seats. He phoned me to ask if I could change his seat for the trip home in case the plane is full. I phone the call centre in Johannesburg and was told that there is no way they can change the seat, he will just have to wait and ask the air hostess if he can change. When asking what happens if the plane if full and there are no other seats, he could not give me a solution. My boss says that the gap between the seats is very small and smaller than any other airline he has been on. He literally cannot sit in the seat as he knees do not fit in.