unauthorised debit

I purchased goods to the value of R212.07. The cashier rang up the goods on her till and I then advised her that I had Club Card vouchers to the value of R29.70 which I wanted her to credit from my purchase. She then cancelled the transaction and proceeded to ring up the goods again but this time deducted the voucher amount and the purchase came to R182.37. However, I noticed on my bank statement that the first purchase was never cancelled and was also deducted off my account. Therefore the first amount of R212.07 was not cancelled and was actually processed as a separate purchase. The cashier then advised me that the amount would be credited back to my account within 24 hours which it was not. I was then told I would have to contact my bank to sort this out as, according to them, it did not go through on their side. Why must I sort out a problem which was clearly caused by the cashier putting through the purchase twice. Now I must have the inconvenience of trying to sort this matter out with my bank in order to get my R212.07 back from Clicks for an unauthorised debit on my account.