KFC customer service has no service to give

I'm a insulin dependent diabetic and it's happened a few time now that when I ask for a sugar free coke I get served a normal one. Not only at KFC but I'm complaining this time because I asked twice when ordering the food, once at the pay window because after paying I noticed they charged me an extra R3 for a normal fountain coke and I asked again at the pick up point but I still received a normal coke. I don't mind the accidental R3 so much. What gets my blood boiling is that it is very dangerous to serve that to me. After I contacted KFC and logged a complain I even have a reference number. After two weeks I followed up as no one contracted me regarding the issue. They then asked for some info and I rep**** with a photo of the slip. It's been more than a week again and nothing from KFC. It's seem they really don't care of they send a customer to hospital due to negligence.