MTN Rewards vouchers with ZERO Balance

MTN rewards, they have an option for their clients to use Yellow bucks points to buy retail vouchers.I bought the voucher,,,,,,the voucher had zero balance,I called MTN call centre, the gave me the Rewards Department,I called the rewards team they said they will refer the query to the IT department hoever they don't have turnaround time for the feedback\solution,i have not received a call from rewards department till now the voucher is still ZERO, I called today , no one is answering the call.