I Bought a lost or stolen phone with out knowing it was stolen

If you purchased it through a 3rd party (e.g., ebay) see if you can get a refund through their buyer protection plan. There is no way to bypass activation lock without the assistance of the previous owner. See: Activation Lock for iPhone, iPad, and iPod touch - Apple Support

It's a hard lesson. Your money is gone.

see:

The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community

Get a refund or have Apple recycle it for free