Bad service

Today I wanted to buy my kids burger meals which is on a special at burger king Cavendish. The special consists of two burgers,two chips,two drinks for a R100. There was no cups available for the drinks and we were told that we could not buy that special thats being advertised due to the issue with the drinks. I ask the manager what she have as a replacement for the drinks and she said that's why she is telling me before hand I cannot buy the product as advertised. She is not giving any replacement.She is just not selling that product.She spoke to me in a firm ordering voice and refuse to give me the product or any replacement. What is my rights as a customer regarding this scenario.

Thank you in advance for responding Unhappy customer Angela Thompson Email I sent yesterday