Burger special but charge full price.

Just had lunch at Red Eagle Spur in Paarl this afternoon. The manager came to serve us. Had a very good meal except for the cold dried out potato. We had burgers like we all know it is Monday burger special. So we order 2 burgers etc.. So we asked for the bill and I had a look at the bill just after we paid. It was rung up as 2 separate burgers and not the special. So I said to her that is there not a special for burgers on Monday and she said oh sorry we did not say special so she went and fix it and I did not have a look at the change again. So the bill with a tip worked out to R240 and she fixed it and came to R167.40 and gave us R45 something change. So she just decide to keep the almost R30 to herself. I don't mind giving tips, but how many people do they rob of ringing up normal burgers and then afterwards go and void it and then rang up specials and keep the rest as their tips. I am not happy at all about this and I'm sure it will be my last visit to them