Bad attitude from cashier, manager just stood ther

Yesterday I decided to go buy myself something to eat from Steers Herm****. I then ordered a combo and literally a few seconds after paying for my order I say to the cashier \please upsize my chips to medium and put on cheese and chilli\" no I can't do that. I then ask a man who works there if I can't change my order by upsizing my chips then add cheese&chilli, I explain to him that the cashier does not want to help me.he says to me \"it is possible to do what you are asking for\"!! He turns around and says the cashier should help me, she says NO..I ask her again to help me or I'm gonna report her and she says \"he has hands too why doesn't he help you he is the manager\".I said again lady I'm not joking please sort this out or I will have you reported for bad behaviour and poor customer service, she says to me \"Go ahead I don't care\" then she bangs the till while helping two young ladies who came after me.Why didn't the manager do anything about this lady? Why did I walk out of Steers without the chips I had asked for even after I had made it clear that I don't mind paying to upsize my chips? I walked away to avoid more drama.I need to speak to the regional manager "