E17 error on Dualview I decoder = New decoder

The old dualview (DSD820 Dualview) decoder at my parents has given up on one of the LNB's and so currently they are faced with singleview, on a Premium subscription. My brother had given our parents his old decoder, of the same model, quite some time ago and so we thought that we would replace their's with his one, which has both LNB's working. We switched over, got everything set up, inserted their smartcard and as was to be expected, it needed the card to be married with the decoder. After some time trying with the call centre, we couldn't get it working and they said I should take it to the nearest Multichoice agent. I took it into the PMB one at Parklane centre, which as a side-note was disgracefully filthy and no one had name badges or uniforms, where I was offered assistance by the clerk. He turned on the decoder and the attendant next to him, quite clearly more experienced, told him that nothing could be done except to buy a new decoder. I couldn't quite grapple with this concept that well, change smart card to an identical decoder and this will never work. Hence I am posting here, hoping that someone from the incredibly useless monopoly of Multichoice will respond.