Vodacom rewards

I received a call from vodacom rewards to say I was a winner. But before I can receive my prize I had to buy ott voucher of R200. After paying I was told I needed to buy another ott voucher R500 to activate my vouchers to receive my prizes. After payment of R700 already now they want another R500 ott voucher to activate. Money I don't have, but they persist.