Poor customer service

I went to buy groceries for my mom who is a pensioner and after scanning the goods and applying a discount the total was R 1388 and then the till stopped working. They printed the slip and ao9the discount again then it showed R1431. The amount had changed and when I explained this to the next cashier she laughed to my face and said I will spend the whole day there. I understand that people make mistakes but disrespecting customers like that is uncalled for. THAT IS WHAT ANNOYED ME THE MOST. It's a pity I didn't get her name but the lady who assisted me with the discount knows her.