Dischem Menlyn won't honour my vouchers

I returned items to Dischem Menlyn and received paper vouchers. I had asked them to make them online vouchers but they said that this could not be done. Why do they give paper vouchers? Others hops give cards I returned items,which they sold but now refuse to refund me. I also have a voucher in my possession the original paper,which expired on the 27th of September.. When I went to buy something they said the voucher had been used ..how? I have this voucher. When you buy using the paper voucher it gets taken by the cashier and you get the change in another voucher. How could the voucher have a R0 balance? I'm waiting for a copy of what was spent on the voucher but still haven't received anything.