Cell C voucher already used!

We bought a R25 Cell C recharge voucher from the Mowbray Post Office this morning and it refuses to recharge claiming this number can't be used.<br> <br> Called their 140 call centre and they claim the code has already been used on 2 Feb. It clearly shows 16 Feb on the slip.<br> <br> Their only solution is you must take it back to the store and try recharge in front of them. Like that's going to work! Oh and we live almost two hours away from Cape Town.<br> <br> What to do? Clearly there is either ***** or a serious bug in their system.