Poor service by rude cashier - Consumer Complaint for PEP STORES

I bought R30 airtime and asked for a cash back, i told the cashier to make it R10 vodacom and R20 cell but she said she can't do that, i asked her why coz i have not yet paid. She said I must go and find someone who is going to do the rubbish that I'm saying. I asked her why is she so rude, she said that is none of my business.I went to another cahier but she turned me down. They gathered together and laughed at me as I'm a fool. I have never been this embarrassed in my life in front of other customers. How can PEP promise us good service and friendly staff but in return we get such disappointing service?