Bad service

On the 10th November I bought a makeup remover on promotion, when I got to the till the assistant billed the original amount and not the amount on special. I queried that and she called a supervisor to void it, she then removed the promotion amount before she could used it and again the punched incorrect amount. Whilst trying to explain a guy by the name of thulani kept on interrupting me saying they remove the promotion amounts, he didn't want to even listen, only when they again entered the incorrect amount he wanted to listen. They waisted 15mins of my time for nothing and again left a trainee to attend to customers alone