Mr Price take money for items they dont have to sell - App issues

Mr Price App does not work properly. The App shows that there is an item available - then when i checkout, they first debit my account then they decide to tell me that the item is not available. I then called them to arrange for the debit to be refunded to me. Since this is a problem with their App and not my problem. They then tell me that there is no way for them to trace the amount that was debitted and that in order for me to help them i must give them my bank statement for me to be refunded. You debitted my account twice for the amounts for R 409.97. This means that you owe me R819.94. AND, the last time this happened you gave me vouchers - I don't want vouchers, i want my money refunded to me.