Promised Cash Back, Now Being Told Stories

I was fooled into joining Virgin Active with a promise that I was gonna get R700 cash back if I joined in October and visit the gym 28 times before the 10th of January 2016. I did exactly that and I didn't get the cash back as promised. I called the call center beginning of February and was told I would get paid on the 15th. Today (17 February) I called the customer care center since I haven't been paid and they are telling me that the promotion was for November even though I was told clearly by the sales guy that it was for October, even your website said the same thing. That is the reason why I joined because I knew I was gonna get the R700 back. Its strange though that they are not paying me but they paid the my colleague that I joined at the same time with. I consider this a breach of contract from Virgin Active because they didn't deliver on their side. So its either you guys pay the R700 you promised or cancel my contract and pay me back my initial joining fee. This is unprofessional of you and I expected better from you.