Overcharged and bad attitude from staff member

I went to the Wonderpark branch of Matrix Warehouse on the 25th of February, I saw they had a gaming computer case on special for R899 which was previously R1699. So I went to purchase it. I entered the store and said I wanted the case but since it was the last one I joked and said they should give it to me for R800 which was R99 off. They laughed I then agreed on the ptice of R899. I went out of the store to fetch a trolley and they packed it for me. when I came back I added 3 case fans aswell at R99 each. I was in a hurry, because i was late for an event, so I then paid the goods and left. I got home and checked my slip they OVERCHARGED me I paid R1797 instead of R1196 like i should have. I phoned and Stanley was not in. I went to the store and a man named Titus said he would refund me the R600 no problem. But I had to come back the next day, I received a call from Stanley on the 27th where he told me that he doesn't want to do business with me again. and he argued with me that he said the case was R1500 whereas it was advertised as R899. which I see as false advertising. During the call he barely gave me a chance to speak shouting at me over the phone. It is truly unacceptable.