Rude customer servise

Not happy at all,I ordered online for burgersfort bubatse crossing n my order was successfully done on the app.then when I got there the cashier told me my order was not processed because I haven't paid yet.i have to wait in line n my order will be processed from scratch. Then what is the use of ordering online if I have to again stand in a line. The cashier was very rude n didn't even want me to show her proof of the oder told me I'm disturbing her she's busy with customers who waited in line. I was very disappointed n will never shop there ever again.