Robbing customers who use vouchers!!!

A very bad experience on my orders where I have had a voucher. When an order is cancelled because they have no stock they do not refund you the voucher, only the difference which has been paid, and you lose out on your voucher.This is ridiculous as the vouchers are earned.I have lost out on R225 rand worth of vouchers over the past 2 months because they don't have stock!! Numerous calls and messages to rectify this and now their response is that they will only refund a voucher for purchases over R500. I have asked for the terms and conditions which states this, and have receive no reply.