Non-payment of hospital bills

I had surgery in December 2015 for which I got pre-authorisation from Fedhealth. Since it was not possible to go to a contracted hospital, I knew I had to make co-payment of R5,000 as per our contractual agreement. However, when I received authorisation, it was stipulated that I had to make co-payment of R10,000. I did that. Upon receiving my hospital bill of R27,952.20, I discovered that I need to pay another R8,006.80 as Fedhealth only pays scheme rates. This implies that I had to pay R18,006.80 out of pocket for the R27,952.20 bill. This was not for a posh private hospital, but an ordinary MediClinic that charges reasonable rates. Why on earth then does one contribute to a scheme for years, and the one time you need them, they drop the ball? I realize that I am only venting my frustration because I feel extremely cheated, but I would like to know if there are other health care providers with a better track record that you can recommend?