Drive through disaster

Used the drive through at the blackheath centre today at lunchtime - i ordered a big Mac medium meal only. When i get pay at the window with my card, i noticed after that the cashier added a milkshake on my order of which i didn't order. I was asked to park on the side while they sorted my refund. I waited for twenty minutes and nobody came. I went into the restaurant because i was running out of time on my break ...only then they could assist me and they seemed confused and really it's not appealing. This really defeats the purpose of a drive through - the convenience and time aspects. This was certainly not a great experience. Assistant manager didn't seem interested either.