Failure to Reimburse

I went to CNA on Saturday 30 September to purchase a Lenovo laptop. Once at the till I swiped my card but before I was asked whether it was cheque or savings, the card said declined and a declined slip was printed. Immediately after I was asked for my pin. I punched it in and the machine said Accepted and it came off my account. Moments later the sales person told me that the card was declined and it doesn't reflect on their system. I was not able to leave with the laptop that day. The sales persons attitude was rude and underhanded almost as if he was insinuating that I do not have the funds in my Acc which I showed him was untrue. I was told to come back if the money doesn't reflect back in my Acc after 24/24hrs. I then only went back today as the money went off my Acc on Wednesday. Today the manager told me that she would have to log a complaint even though I had my bank statement and profit of the transaction. She said she could not reimburse me because she needs to double check with her help desk. I was appalled at how easy it was for them to take my money but they can't give me back my R4000. Really disgusted at the service and manner in which my case is being handled.