@Shopaholic :
Well, that still sounds like you have proper, legal, title to the device.
(The process the seller goes through assures you of that.
At least in the USA and Canada is probably very similar.)
You will have to deal with Amazon Customer Service to get the ownership change recognized by the registration process.
Big Note:
The first level C.S. contacts do not have the required database access to fix this problem.
So it will be a long repeated series of:
*) Explain what happened (offering copy of purchase receipt).
*) Hearing "we can't do that".
*) Asking to speak to that level's "supervisor, manager, boss, whatever"
*) Repeat from #1 above.
*) Eventually, you will get high enough in the organization's food chain to reach a person who can do something about this.
*) If (when?) that fails, you will have to start writing letters.
Until then:
Just keep it in "airplane mode" and use those features that are available in that mode.
Note: Only a very few of our Kindle add-ins require any network access.
So nearly everything you find here will probably work just fine.