It's a general problem with used hard- and software which need registration for support. If the former owner don't cancel his registration, nobody at Arturia would know if the new request for registration is correct or maybe from a stolen product.
The cancellation of registration should be part of the bill of sale. If you *have* a bill of sale or a link to your ebay auction where you've purchased it, then sales support might be happy with a copy, but this is not standard.