Bad customer service

I was at the mall Debonairs Pizza, at Eyethu Mall in Orange farm. I was assisted by Magugwana Thabile.

I bought 1 Small oizzq BBQ Chicken and asked her to add a Buddy Stoney for me, upon realizing that the buddy was abit costly for my budget i asked her to please change it for ke, she then told me that i can't make changes, so i asked her what if i don't have money what's gonna happen she said i don't know but you will have to pay for it cause i can't cancel the order, i asked her how is it possible that you can't cancel an order that you haven't even really paid for.

I am very so much disappointed that i added paying for something that i did not want, nor had money for this is just so inconveniencing in so many level and very disrespectful.

What kind of a store will restrict people from actually making slightly changes in their order.