Mtn has faulty vouchers

I bought R30 airtime voucher from a supermarket, and then when I recharged I got 100 SMS, which is not what I wanted so when I called they told me that the airtime voucher is faulty and that they will investigate the matter as they can see the airtime is still not used, so now I have to wait for investigation which can take the whole day to fix, I need to use the airtime urgently but now I'm told to wait- I'm not impressed with how they handled the Query , I expect them to recharge my account not make me wait because it's not my fault and they say that I might have to go back to the store where I bought the airtime which will be another expense