Pathetic Service Forcing faulty device to customer

I bought an sound system in July at HiFi corp. Within 3 weeks the device could on switch on. After an hour of, I gave up returned it to the shop booked it in and when they tested it, it worked. After 3 weeks the again on the 30th of September it stopped working recorded a video, the whole week I would test the device and would not switch on. on the 5th of October I took it back to HiFi corp and they booked it in, tested it and sent it to Sony. We were promised that sony replies within 2-7 days and no one called for 3 weeks. On the 26th of September went back and only to be told that the device is working and that it was due to customer negligence that it was not working. We refused to take it back due to that report and the fact that it was tested and did not work even at the shop. how could that be negligence. I told them I would not take it back and would only accept a different device since this is the second time this has happened. Now we are being forced to take that device as she said what are they going to do with that current device.