Onair Tv refuses to help customer

I was contacted via telephone of this deal to purchase an Explorer decoder with a HD decoder for a monthly fee in August 2015. The new decoders were delivered to my house by a courier on the 06 August 2015. An installer came to install it on 14 August 2015. On 17 August, I contacted On Air TV to complain about the HD decoder not working properly. They said they'll send out the installer to look at it and if it was the decoder they will replace it. The installer came a week after that and the fault still persists after that. I called again and the installer came out again and after he left the fault was still there. I phoned again on 26, 28 October 2015 and they said they'll send the installer who never pitched. I asked them to cancel the deal as they are not interested in fixing my problem with the decoder. I asked that management give me a call, no one called me up to today. Today, 07 December 2015 they want me to take the decoder to DSTV to see if there is a problem with it. This is a new product and I should not run around to get it fixed.