Norton 360 eBay purchase fraudulent? & can I change the registration?

I purchased serials for Norton 360 on eBay from what looked to be a reputable store.  It included 1 licence for 3 pcs.  I used the key on my laptop without a problem.  Tried on my desktop and it said all keys have been used up.  Contacted the seller and he said he would contact his supplier to look into the problem.  Created a claim on the Paypal resolution center for protection. The next day he somehow reset the available slots for me and I have now enabled Norton 360 on 2 computers.  This seemed odd to me the seller could reset the available slots.  So I checked my online Norton account to find it is not registered to me, so I cannot control the one year licence I purchased.  It is registered to an email which I believe is the eBay seller of the key.

Through the resolution center I contacted the seller again to explain my findings & to possibly get the key registered to me so I can have full control of the product. 

Unexpectedly the seller has given me a full refund without explanation and so far he hasn’t cancelled the three available slots again. 

 

My question is, because the keys were registered to an unknown party, would they be able to access online backups or any other Norton 360 feature for their personal gain? Also can I get the product switched over to my Norton account as it stands now?

And what could be the risks of continuing to use the key while registered to the other party?

Thanks