invalid unipin voucher.

I bought a prepaid voucher from a local grocer, which from whom I always buy my pre paid unipin vouchers. Last night I wanted to load the voucher, and I kept saying ' pin not valid' So emailed ********** and also sms the support line. Nothing, no assistance since this morning. Finally a rude person by the name of Chevonne Van rensburg, send me a short mail saying, that the store which I bought it from should replace the voucher. How? they get this vouchers from you Unipin. How are they at fault. I did not spend money on pre paid electricity for nothing. Just shows you, anything related to Eskom is a mess. I demand this fixed.