Cashier not paying attention

I was with my mom today at Jetmart Newcastle before leaving. The cashier said to my mom she has received an increase in her credit of which my mom and I were deciding she must decline it however she had already accepted the credit increase and we had told her to decline it then she said we have to go to Edgar in order to be helped with contacting their head office so that they reverse the credit limit acceptance. I had no time to do the run around because we were not at fault she had to make an effor of which she didn't then I bought papers nappies on promotion for R139 however when I left the store i checked my reciept only to find out that she had charged me the normal price of R189 this is really day light ******* to customers cos she didn't even tell me how much my purchase came up to. I am very unhappy with all of this and I'm sure I'm not the only one who's been overcharged and for my mom just because she's an elderly woman this cashier thought she can just make a decision for her. Since I'm in joburg I'm wondering how will I get the difference that I was supposed to have saved when purchasing those papers nappies. Code 00039 Trm00044 Trn 119227. Train this cashier properly!!