Faulty Decoder

I had signal issues with my decoder and I went to multichoice branch in Thabong Sebokeng Shopping Centre and I was advised to bring along the decoder for the technician to asses and confirm if wether the problem was with the decoder or satellite dish. Technician confirmed that the decoder was fine. And they made me pay R250.00 for the dispatched technician to my house. Upon arrival at my house they have now realised that it's actually the decoder that is faulty. And thiey refusing to pay back the money.money by telling me that there is no refund. They failed to show me those terms and conditions.For having failed to account and take responsibility for the wrong diagnose on the devise. I have paid for nothing. And I'm still without signal. Now they tell me I must buy another decoder as this one is completely damaged. I demand an answer for my query. If I don't get the response within 48 hours I'm sure you not gonna like I'll do next.