Just upset with wrong order after they repeated it

at 12:07am on 21/03/16 myself and my gf had gone to steers, we choose to take 2 big bacon king steer burgers well just the burgers cause we wanted 2 medium cheezy chips with our order. We did not take the combo meal cause the main purpose of our visit to steers was to get cheezy chips. So we ordered just 2 burgers and cheezy chips i also have my gf as a witness to this. The lady at the till repeats my order which is correct so after paying we wait. Once we see the food being put into the bags i realized that the lady put normal chips into the bag. I had then asked her that we asked for cheezy chips and not normal chips, she then asked to see the slip which she then pointed out to me that its normal chips. My frustration grew as she clearly repeated the order to me and i confirmed and yet still managed to get the order wrong. My gf and myself was upset we just took our order and walked out. What was the purpose of me ordering normal chips with my meal if i wasnt going to take the combo???? After we ordered we went into the shop and bought buddy bottles of cooldrink this can be verified through the cctv footage from the shop. Why would we do all that if we wanted normal chips?