I had the exact same experience. I emailed to return the nexus, did not get a response. I called them and they said they would set up a return, then I didn't hear anything. I called them again and they told me I past the deadline to return the tablet so they couldn't accept it. I then spent an hour arguing with them that I had started the return process before the deadline and that it was their lousy support that put us past the deadline.

Finally I just had to be obstinate and say "I want to speak to your manager." over and over and over again until I got to someone who knew how to look up my support ticket and see that I had started the return process before the deadline. Eventually they sent me the info I needed to return the device, but by that time I was so scared I would send it to them and then not get a refund that I chose to sell it instead.