Rude waiter at wimpy Myezo Mthatha

I went to Wimpy with my friend and her boys. We wanted to pay with the Fnb App bt we were nt sure what is covered so we asked the waiter and she came with the response saying that everything on menu is discounted. We choose to buy desert. When were about to pay our discount was diclined. The manager said she explained to the waiter that only burgers that are discounted we told her that we have asked and the response was everything on the menu is discounted. The waiter came very rude saying that we must not pay she is gonna pay. And she was shouting at the back as the kitchen is near the counter. She did not even apologize to ask. I have never seen such a rude employee in my attire life of customer services.