Discovery vitality voucher at pick n pay scottburgh

I am on Vitality and got a R100 voucher to use at Pick n Pay Scottburgh branch for my grocery shopping. We put R100 worth of groceries in the basket. Because we don't have vouchers very often I asked the lady at the till if we scan the code before or after the transaction. At this stage she had only scanned R28 apples. She called over the manager who put in the code and gave me a receipt. I asked her what about the rest of my items is the balance on the slip and they started to panic because they realised the code did not work for the rest of the items. I asked them to please phone discovery and find out how to fix the issue. She told me to come back the next day which I did. She then got someone else involved who took down my details and said she would phone me. After not hearing anything for 4 days I went back to enquire only to be told there is nothing they can do to help me. I am in real estate and earn by commission only. I don't have the money to throw away and could really have used that R100 voucher. I am disgusted at the service and the fact they couldn't call me and haven't bothered to try assist.