being ***** and ******obbed

Hello my mom went to a pic'n'pay store in germiston to do a Mini grocery she went and bought for R155.50 and payed using two hundred notes but the lady at the till punched in R190 and the change amounted to R34.50 which she didn't notice it till she arrived at home I don't think this was a mistake cause honestly speaking if your a cashier and someone buys for R155.50 and gives you R190 you'd simply give them R20 and continue with the transaction. So I decided to call the customer service help line they put me through to the manager DAVID and I explained the situation he said he'll go check at the till and get back to me which he didn't and I called him the following day he was rude and told me to come fetch my R10 I asked him to give me his senior email address he gave me the wrong one or something cause it didn't work and I'm going to attach the slip so you can check and see how people are being ******