Disgusting treatment and service on their mistake

I'm thoroughly disappointed and disgusted by how I was treated at Observatory branch in Cape Town by both staff and the manager. My order was taken down incorrectly after the person repeated everything I said. The order screen did not work so I had to ask for the total amount. After this I payed and was asked to go sit in the grill bay to await my food which I did with no problem. On receiving my food I noticed a meal was missing that was quoted back to me on the screen. When I confronted the staff at the drive through window about this they told me it was my own fault I didn't check it properly on the screen when in fact the screen did not even work. I then asked to speak to the manager to see how this problem would be rectified to which he told me he was running a business and that I had to pay more money for their mistakes. My boyfriend then asked for the managers name which he uttered under his breath and also asked if he had a name tag so that we could take a photo and he gave us attitude and just told us what his name was again. We then asked if there was a regional manager that we could bring this problem up with and were totally ignored. I walked away without my food.