Terrible customer service

I was at Kuai yesterday late afternoon, I placed an order for a smoothie. After 5minutes or more a couple placed an order as well. 10mins after that they received their orders and still I hadn't received mine. And 2more people after them. I called the waitress who was giving out orders to find out what the delay is as it had been 20mins. She didn't explain much, just went to the back. A few minutes later I went to the till to get my money. Only that time were they busy with my order. I asked for my money back and the lady at the till gave me attitude(which wasn't the first time). No explanation, no apology she put the money on the counter and asked to help the next customer!