No one said that you stole it. But it appears that it was stolen nontheless, and anyone with stolen goods, even if purchased unknowingly and in good faith, usually has little recourse. When you buy from eBay or any other unauthorized source, there's no guarantee that the person you purchased the item from didn't steal it, and since your iPhone has indeed been reported as stolen, that seems likely that the seller did steal it, or got it from someone who did. You may well be an innocent party, but being innocent in this case doesn't get you much of anywhere. You'll need to see what PayPay will do, if anything - doubtful, but you can hope - and continue to try and work with O2, Orange and the police. You may well just be out the price of the iPhone.
Good luck; you'll need it, I fear.
Regards.