Extremely bad service!

I went to Game Fourways on 1 July 2018 to buy a DSTV decoder DSD4136 for R299 as advertised on their website. I was taken to the paypoint to make payment. After making payment I was told that they dont have stock. After being helped by, I presume a manager (African Male) he said as they dont have stock and the decoder DSD4137 is R399 he will give me the demo/display unit of the DSD4136 for R299. Upon receiving it I exsplisitly asked him if it is in working order whereafter he confirmed that it was. We had an installer at our property this morning (7 July 2018) in Lephalale to do the installation. We then discovered that the power adapter was faulty, we used an old decoder's power adapter for the decoder. We then phoned in to the DSTV callcentre to activate the triple view for this decoder only to be informed that it can't be activated on my name as it is already registered on someone else's name. The callcentre agent advised us to go to our DSTV outlet to sort the problem out, they were however unable to assist and told us to go to Game and get them to sort this out. I called the Fourways Game branch and a Maureen (floor manager) advised me to go to the Lephalale branch and they will replace it. I went to our Lephalale branch and they confirmed they don't have stock. The staff there was not very helpfull and infuriated me. I explained to them that the installation for the DSD4136 was already done at our premises and is different to the DSD4137 and that I am not willing to pay again for the installation to be changed. I then again phoned the Fourways branch to try and get help again, I spoke to an African male who said he can't do anything about it and that they shouldn't have sold it to me in the first place. I am extremely frustrated with the situation and infuriated by the fact that I have been sold a decoder that was probably returned due to a faulty power adapter and that no effort has been made by Game to help replace the decoder. I have been refunded but this still does not sort out the problem with the installation as I have been told that the DSD4136 has been discontinued. Should I not receive adequate assistance, I will escalate this to the consumer board.