Won't refund or exchange faulty wifi router

I ordered a wifi router which was faulty. I returned it only to be told that after testing it was found to be working. When I asked if the actual problem that I reported was tested you said you didn't have the facilities to test that, and that I must pay to have it returned to me. I was told that I must go and test it again, but I already did that before I returned it. Why would I want to receive a faulty router back? All I want is either a new working unit sent to me or a refund. You've had the unit since 11 November and there has been no progress since. You don't respond to emails asking for an update. Please can someone sort this out. Pathetic customer service.