Nandos poor customer treatment

Very disappointed with nandos Newlands, Inanda road branch. I am a local businessman and support them very often. I normally buy my food and cool drink from them however I went to the bank first and bought a cool drink after I finished at the bank as I was thirsty. When I got to nandos to order the food, they say I'm not allowed to bring my cool drink in. Which is unfair because I already had cool drink and I'm buying the food from them. In future I will go elsewhere. There is a kfc next door and I can always drive to the next neighborhood for food.