Telkom 10th birthday promo

Hi guys so telkom says they are running there 10th birthday celebration where when purchasing airtime or data they send you a voucher which you can redeem by dialing *120*78910#. I have bought data plenty of times and each time I enter the unique code send to me it says the voucher has been redeemed already.... So it is of my view that the company responsible for running ou g the promotion is redeeming the unique codes themselves or we are just being **********. U try and call to notify them of the issue and can never get hold of them