Paid double for one meal

I paid double price for one meal. the waiter gave me the bill and I went to the teller and paid R100 including tip. I was in a rush I did not wait for my slip. After I have left Derrick came running and said I did not pay. I told him I gave the bill and R100 to the guy who was processing the bills at the machine. He did not believe and he said I should identify the guy and I could not since I did not see his face coz he was busy on the machine/screen. To avoid embarrassment from the waiter I gave him another R100 and left. he said he will view the cctv camera and I should return. unfortunately I didn't want to waste my time and petrol driving from Benoni to Centurion for R100. I believe that's how waiters are conning people by accepting other's bills and not process them. Im sure they gave each other R50. As much as I love their wings I will never go to Spur again