Pick n Pay no business selling Roblox vouchers

I purchased 2 Roblox vouchers from Pick n Pay at Princess Crossing. None of the voucher numbers or serial numbers are valid. I went back to the store and was addressed by the store Manger who informed me that I will not get I refund. I did not request a refund, I wanted assistance to get the correct voucher numbers. I was told he would call be back. He did and I missed his call. I have since tried calling him numerous times. No one answers . I would think if he hasn't given me feedback that he would try calling me again, but nothing. This has been going on since the 13th of March.