*******ly charged 15% when I requested a refund

I bought an HP laptop on 03 April at the Sandton store. I noticed that the speed was extremely slow, I gave it a chance and the next day while surfing the net, the speed had not improved. 2days later the laptop was extremely slow so I called the call centre to ask if I could return it to any store or to the specific store where I purchased it and they confirmed any store. I went to the Cradlestone mall store, but didn't find anything I could replace it with for that price. Not finding what I wanted I left the Cradlestone store and the next day I wanted a refund so went to the Clearwater mall store and they told me that because I'm returning the laptop at the store I didn't purchase it, they would charge me 15% off the original price. I refused and rather drove to the Sandton City store. The tech staff and store manager at the Sandton City store told me that they would still charge me 15% which equates to R1 434.65 because I had broken the seal (selotape) of the box and referred me to their refund policy on the slip. The policy states that a 15% fee is charged upon return if the goods are not in their original packaging and condition. I brought it back in the original packaging (only the selotape was neatly torn to open the box) and the Tech staff confirmed the original condition. My question to the staff members was "How was I going to know that the laptop is slow if I didn't open the box"? I see this behavior by Incredible Connection as ******* to charge a customer 15% for wanting a refund on a product that is not satisfactory.