Voucher issues with Debonairs

Good Day I have purchased a online voucher for Debonairs , when checking out i app**** the voucher which reflected before i could check out, once i checked out the voucher disappeared and the full amount was displayed . I was now liable for this amount even though i used my voucher. The voucher is now invalid , Yet i did not receive any of the voucher amount , which means Debonairs accepted my voucher then removed the voucher amount and expected me to pay the full amount . How pathetic as for the customer service option on the website is absolutely useless , why does it even exist if there's no support there . I want my voucher refunded