Did not receive my order in full

I went in to buy my kids some food and I bought myself a Tall Latte, only to get home and find out that they left out my Tall Latte, called McDonald's in Centurion lifestyle center and the guy told me that I should come fetch it. They expect me to use my own petrol for their mistakes. I told the guy I want a refund and he still said that I need to be in the store for a refund, I mean who does that, who doesn't know that they are causing an inconvenience by not putting all the things you ordered in your actual order.