incorrectly supp**** goods

I purchased a dstv HD model 4u decoder online from Kalahari. When it arrived, I contacted multi choice to set it up. They connected the decoder for me and activated it. When they asked if the decoder was model 4u, I said no it is model 4s. The next day I checked what I ordered and realized that I was sent the incorrect item from Kalahari. I contacted them and after much running around from pillar to post, they finally said they cannot refund me because I already used it and if they do take it back, I will not get what I paid. I explained that it was their fault as they supp**** the incorrect item but they still remain defiant and do not want to refund me for the incorrect item supp**** or compensate me for the inconvenience. I am very annoyed with Kalahari and their attitude towards the situation. Poor service, wrongly supp**** goods and no feedback when call center was contacted.