As advised, try your payment provider and definitely report the seller - 'reportfraud' now handle such reports.

With the number they provide for your report, and any evidence you have that the item was stolen (can you get an email from Sony to confirm this?) you should win a chargeback.

For me, the fact that the seller was a private seller with lots of new phones would have been a red flag.

Although they have a good amount of positive feedback, they have only been active on Ebay for a year and are trading illegally from a private account.  Business sellers have to allow 'any reason' returns and must display their business name and address.

Check who you are buying from.