I have received my (used) Edge on Wednesday. I tried to register it and I got the usual message (the device is already registered).
While I sent an email to the person who sold it to me asking him to unregister the device, I also posted a support ticket at Support tab.
Even before my seller replied, a staff called Junie kindly replied asking for my serial number, and offering to transfer the question to Tier 3 Support level.
I replied back with the S/N and in 15 minutes (!!) my EE was ready for fresh registration, and I had to write the seller asking him to forget about the whole thing.
I was amazed at the fast, efficient support. It's the first time in 25 years with computers that I get such a fast action to solve an issue.
So I would suggest that you kindly insist, based on my (and other's) encouraging experiences.
Good luck with your problem.