Why does the conductor refer to Valli as ‘madam’?

When the conductor stretched out his hand to help her get on the bus, Valli said commandingly that she could get on by herself, and that she did not require his help. She did not act like a child, but as a grown-up girl and therefore, the conductor called her ‘madam’. When the elderly man called her a child and asked her to sit down on her seat, she replied that nobody was a child on the bus. She kept stressing on the fact that she had paid her fare like everybody else and therefore, she should not be treated differently.