Nasty Attitude Cashier

KFC Perpergroove mall Grahamstown service is horrible I was making a purchase through the drive through when after inserting my pin swiping for my order I realised I wanted to add, I then ask the cashier to add and she so rudly told me I have to go back to begining and Que they don't process two order from one person. The attitude stinks I'm very disappointed in the manner the cashier spoke to me .