Hi-Fi Corporation passing the buck

I bought a Dstv Explorer from Westgate Hifi corporations on the 2016.04.24 . On the Monday 2016.03.28 I took it back because it doesn't work. I spoke to Petter at Hifi corporations Westgate store and he said that he can't exchange it for me that day because he has to have it tested and the people that have to test it is not on duty that day. I said that's fine and left the decoder at Westgate Hifi corporations. On Tuesday he phoned my wife and said that he have to send the decoder in to be tested .Now on Wednesday he phoned again and this time he said that we must come and collect the decoder and have to take it to be checked by our self's . I bought this product at Hifi corporations Westgate and now they want to pass the buck. After they said 3 times that they are going to send it in . My proof of purchase shows Hifi corporations and I expect them to sort it out for me,not any one else .