Why are foreigners over charged in S.A hospitals

I was admitted at rosebank hopital on the 21st of June in the morning for an arthroscopic surgery. I am a foreign patient from africa and I am NOT on medical aid. I spent about 30mins to 45mins in the theatre and I was discharged the very same day in the afternoon. My complain is that the hospital charged me 31,000 rands and the doctor and the anaesthetic charge was 20,000rands plus consultation , blood test and other charges were separate. So in total the bill came to 50,000 rands plus. I was made to pay cash prior to the surgery. After consultations with relatives and friends who live in S.A i was told by them that i have been way over charged! I feel I have been cheated and this is gross unfairness on my side. We foreigners come to S.A for medical treatment out of desperation and we are a working class. I feel I have been cheated of my hard earned money. I am very disappointed and would urge the authorities in charge to look into this matter.