Cell C Duplicate pre-paid vouchers "**** or not"?

Pre-Paid airtime vouchers,will not credit number!Phoned customer care told voucher used on 23 march.Asked how possible as opened today(25 march)was told it most likely a duplicate print,in other words there seem to be a number of vouchers with same number(how many?)Told to get refund from vendor,surprisingly he is not interested,is this a **** on a massive scale.