Unauthorized transactions and Nedbank would not assist

I made a card purchase at westgate mall shoe city and my card declined with no reason given. I then made a cash payment and after I left the store, the transaction that was declined went through on my account and now I have paid double for my goods. I called the store aswell as my bank NEDBANK to assist me and it seems no one is able to.the bank says I must speak to shoe city and shoe city says I must speak to the bank. It seems my money just disappeared between the store and the bank and no one wants to assist me. O asked my bank to reverse the payment and they refusing. The store as well as their head office and supervisors are very rude and would also not assist. Will be changing my bank and will definitely not advise anyone to buy from shoe city.