Rude receptionist

I have been visiting the Spur at Gateway from inception and I have always enjoyed my experience. My last 2 visits were unbelievably horrible. I went to get a take away and on both occasions I was assisted by a lady by the name of Leah. I have never come across a person so rude in my life. She never greeted, asked me what I wanted, and i ordered, she processed the order before me even finishing so I had to ask her to add mushroom sauce. She then hands me the receipt when I noticed I was charged R40 extra, when I brought that to her attention, without even an apology, she grabbed my receipt and started banging on the computer harder(maybe trying to change the order in frustration). I stand there for a further 5 minutes till she hands me my receipt(the incorrect one). How are you at front of house and you have no people skills. How do you show your frustration to your customers!?