Is it a code you're prompted for when starting up the phone? If so, the retailer knows absolutely nothing about phones, since there is a way round this. I have PM'd you instructions on how to fix this. If this a different issue, let me know.
Just a side note - we do already have a forum topic on this on the first page of the Sony Ericsson section. You may have had a better chance of a responce if you posted in there