Won a competition and Capitec won't honour the prize

I received a WhatsApp communication from Capitec Verified WhatsApp channel that I have won a 12 months voucher from their win a share of 350K in prizes when you purchase vouchers on the App. I was chosen as one of the winners and they stated they will send my voucher in the next week via SMS. A week passed and I decided to checkup with Capitec via WhatsApp which was pointless. I went to their Facebook DM and an agent who attended me comfired the competition and my win but said I must check for the voucher in the App under Perks. I send screenshots of my app to the agent showing that there is no Perks in my app and no voucher anywhere. She then said I will get an SMS in due time as they are still investigating what happened to my voucher because I have indeed won. The shock I got after these responses. I mean you run a competition, you notify a client they have won and you go silent. When the client follows up on their prize you send them back and forth and when you see she won't let it go without answers you resort to the "we will investigate". I am smelling a dead rat in this competition proceeds by Capitec. I want my 12 months prize and I will not let this go. ******* Bank