If you're interested, check out the following site for a decent database of DVD unlocks. It's got a few machines that other sites don't feature, so I'm recommending it. It seems a good place to go for those rarer machines by the looks of things.
It's actually got a Sony unlock code on one of its front pages. I don't know whether it works though, as I heard Sony machines can't be unlocked with a handset? Anyway, here's a link to the free page - the DVD codes might be of some use to you.
I have exactly the same problem. Bought it also a year ago, and I did start a complaint and refund procedure on e-bay but ofc the user that sold it just disappeared. I've bought and tried several methods but nothing worked so far. The method supposedly to work for the DDX-7015 was : * insert DVD, wait for the 'region code error' to appear * turn off using src * turn on using src and hold play for 10 seconds
It didn't work for me, so doubt it will work for you, but it's the only method I've found online so far...