1Voucher *****

I bought a voucher for R4000 from them on 5th June, paying by credit card. When I deposited this voucher at a vendor the answer was "voucher used already". Countless emails and telephone calls to them resulted in promises, but no refund. They actually sent me a email saying the ticket has been resolved which is a intentional lie. Surely this is *****. Any suggestions on how to solve this problem?