Bad customer service, rude tone

I just phoned the customer care regarding my account as my installment is R615 I normally pay R700,and I wanted to buy with my card but it declined instead of the agent explaining to me,she said am I dumb?? Why can't I understand and went on too,saying must she spell her name?? Her name is Olowalo?? Then hung up...This is far the worst customer service ever.