Rude over the phone

On 2016-02-26 at 12:30 my grandmother was in the shop to withdraw money that i transferred at Pep PMB. She misunderstood and thought the money was at Shoprite as we used to put it there but this time there was no Shoprite close to me so i used Pep and they said she can withdraw at Shoprite. She called me saying they were unable to help her so i ask to speak to the cashier to ensure that the number were correct but the cashier just bite my head off telling me how stupid i am for playing with my granny then she dropped the call, i called again asking for my granny but she carried on talking to me like a stupid mad child that asking her for help. I've Neva been so disrespected by someone who does't see me. And i have a feeling that how she treats people in the shop.