MTN Rewards/TLC rewards has the most disappointing customer service

I am experiencing some difficulties with redeeming my voucher from MTN Rewards/TLC rewards and would appreciate your assistance in guiding me through the process. When I redeem the voucher, I receive a message stating that the voucher code is invalid. I have sent numerous email and have not yet received a response. The initial email mentioned that I should expect a reply within 48 hours, but I have not heard back. Request no is ***