Bad customer service

So me and my friend we visited nando's on the 1st of December 2021 during lunch time and ordered our meals after couple of minutes we saw a special and decided to exchange the order, we ask one of the waitress to do so, then she went on to enquire unfortunately she came back and said that it was impossible, thus when we said we rather cancel the order and go somewhere else, the suppose manager of which I assume he was took the slip to the cashier by the name of Mpumi who was a nightmare in daylight started complaining to other customer directed to me saying that people who don't know how to read menus are nuisance while I was still standing there waiting to be assisted what kind of customer service is that, lm really disappointed with such a renowned company like Nando's, l will never go back there again