Failure to honour reward voucher

I received a Discovery Health Vitality rewards voucher for R500 for Cape Union Mart - as a result of a bonus spin reward for meeting my goals three months in a row. The voucher showed up on my cellphone and when I went to claim it at Cape Union Mart - it had vanished from my phone. It had been on my phone earlier in the day . I noticed in the week before that the expiry dates got mixed up but then did correct. When I phoned Discovery to query why the voucher had disappeared, they said that there was no record of it - insinuating that I was a ****. Philip, whom I spoke to said he would get his supervisor to call me back. More than a week later, nobody had called me back, so i called them and spoke to Vuyo. I questioned why they didn't keep records of awards allocated, but he also insisted that no such reward had ever been issued to me - once again insinuating that I was lying. When I had called in the first person I spoke to said that they had been having issues with the App.