My account was doublecharged and still not revrsed

I claimed back a phone from my insurance, I had to pay a R300 extra which I asked then to take it from my credit I have available. after a few weeks I received a statement which shows I have made a purchase of R600 at the store when I only asked her to swipe the R300.00 call the head office to enquiry about my account and the told I need to refer to the store due to purchase was done there. I had to take my lunch time any take a cab and run to the store due to their could not help me on the phone. After a 3 days I had to call the store and ask for updates no one bothered to call me and update me. I sent all documentation they request from the and told me they have resolved the query. I called head office to confirm if it so, they confirmed the is no change the R600 is still on my account. Now I have to pay for stuff I don't know with interest and still have the store lying to me telling this has been correct. I want this R300 reversed with its interest. and I want my money back where I have to run around to fix the store's fault. I see this a ***** and if this is not corrected with in this week I am opening a ******** case against the store. how may people do the they do this to?