Disgusted

I am extremely dissatisfied with the way I was treated in Shoprite Athlone store today.I had three R10 vouchers that I redeemed from Cell C for Shoprite Checkers and wanted to purchase a R12 airtime and two cooldrinks for R18.The first voucher went through but the other two didn't and I was told that I owe the cashier R8 as she rung up the two cooldrinks at a cost of R18.I asked if I couldn't take something else for the R10 instead and was blatantly told no I am going to lose the R10 voucher if I could not pay the R8.I am so sick of the way Shoprite Athlone treats a person.It is not the first time I'm getting bad service from them.