Cashier sign = You cannot pay here??

I visit this branch of Dis-Chem monthly. There are 2 cashiers, 1m apart in the over the counter area. Seeing the sign, clients stand in a queue. When my turn arrived, the cashier asks me how she can help. I said I want to pay & she rolled her eyes & told me that payments are done only at the other till. I told her that she should have said something earlier when she saw me in the queue. Her reply was that I should have joined another queue earlier. I said that there's a cashier sign above her head, explaining why I stood in line. She raised her voice & said \so why didn't you read the other cashier sign?"So I joined the next queue & paid. I"