Telkom doesn't issue valid vouchers / no refund

My mother bought last week a Telkom mobile voucher from Pepstore and since then she can't redeem this voucher We phoned, been assisted on whatsapp and even went into Telkom store, but nobody can assist. We've been told to go back to Pepstore, but Pepstore says they cant do anything as the voucher was generated by Telkom and they have no control over 3rd party suppliers vouchers - this makes sense. The problem sits with Telkom, but absolutely nobody is assisting us. This voucher was R149 and my mom is a pensioner, this is money she doesn't have. This is nothing else but ***** and theft. How can Telkom sell vouchers with invalid pin.