I have a complaint against Pick a Pay Mokopane, Limpopo

I have a complaint against Pick a Pay Mokopane, Limpopo. I redeemed a voucher on 6 September for an R1000.00 at 15H37. they told me the bank declined, On Sunday the 7th, I went to Nedbank ATM and was told Voucher already used. I did some follow up from the company that sent me the voucher, and they confirmed the voucher was successfully withdrawn from Pick a Pay Mokopane on the 6 September at 15H38. I went to Pick a Pay Mokopane, and there is no Manager on duties. To assist me, we had the same problem before with a colleague, and we got no assistance. I am not happy with their service as they just don't care about assisting loyal customer. I do shopping with them every Saterday, and spent 3 to 4 thousand a week, this does not even include the dailie odds I buy