I had exactly the same problem, just that is it about 1cm from the top of the screen. Very strangely, it disappeared after a few restarts, but then changed into a bad patch of pixels at the top right hand corner. Refer to the picture in this thread.
https://www.mobileread.com/forums/showthread.php?t=7266
They finally agreed to do a replace, after 1 week of correspondence with them. Yes, email doesn't work unless you have called them to get ticket number.
BTW, what's your order number? Mine's #858.