Bad Attitude from Pep Cell Cashier

I have never ever got bad attitude from Pep Stores but the cashier. I am from ndofaya mall and I just bought a 1foru voucher well I didn't know there is no R30 voucher but only R20, the cashier Swazi from Pep Cell couldn't explain that there is no R30 voucher she made a noise and rude remark and I asked her to not be rude but explain that she doesn't have what I'm asking for. Please advise your staff that they app**** for the job and they should learn good communication skills I was seriously not impressed. Her name is Swazi.