Refuse to give me my cash back that is due to

I wanted to join the gym but missed a special that virgin was running on a R700 cash back if you come to gym 24 times in two months you get a R700 cash back paid into your account. A month later I get a call from the sales guy Mbulelo saying that they have extended the special but only for the first week in Dec. I joined because of this cash back deal. I only had half of the time to work in all my days to get my cash back in February and I did it BUT I never got my money back! According to them I was short of one day! This mistake could even have been made on their side but they refuse to pay over my money. I had half of the time that the other members had to make up the 24 days as I only joined a month after the promo started but I still did it!! Nobody is interested in helping me sort this out. I want my R700. It's a week later and I'm still waiting for the manager of Virgin Active Benoni to get back to me with a resolution.