Mr price Taking vouchers without reason.

I bought a size 32 jean skirt online that i needed the Saturday so i collected on the Friday only to discover that the skirt states in the inside size 30 and the label states size 32. So i went and returned it. the skirt i than took was cheaper so for some reason they could not give me the remaining balance in cash so the gave me a gift voucher for the remaining balance. I wanted to place an order online and added the voucher for discount. I proceed payment but entered the wrong OTP pin. They cancelled the order so i reordered the goods and when i wanted to enter the voucher again for the discount they took the cash on my voucher. i phoned them the would have fixed it i even what-sap them but still nothing was done about my voucher. So i paid the full amount for my order. HOW CAN YOU TAKE A VOUCHER FOR SOMETHING I DID NOT BUY OR EVEN USED THE VOUCHER FOR|?????????????????????????????????????????????????????????????????????????????????????????????????????????????????