Unhappy Nokia lumia 1520 demo version

Hello
I recently bought a Nokia Lumia 1520 from eBay, in spares and repairs. The seller said that it doesn't get signals in UK, but when I got it, it came out to be a demon version.
I sent the phone to Nokia repair, it they said that its not in warranty and BER- mom tech.
They said that it might get repaired from a third party dealers, but Nokia can't do not.
Now what to do? What can I do to make it a normal phone.
Oy does catch WiFi signals and has a genuine IMEI NUMBER.
I am not really good I'm tech stuff, so please guide me in a little detail.thanks