Without a legal path from the original owner of record to you, which you
could then take along with proof you actually also are a legal owner, an
Apple Store will not open or unlock the iPhone or any protected iDevice.
The recourse would be to see if whoever sold you the device would take
it back. Since one cannot tell the legality of that transaction, that is the rub.
Sorry, there is no alternative of activation lock or some stolen notice other
than undisputable proof of legal ownership. If someone passed away, the
relative or legal overseer of their property would have had to make a plea
to Apple in order to see if they could open or unlock the device.
Had you bought this item via eBay or auction site, some of them give you
options if the reseller does not accept returns; the site would refund to you.
Good luck in this matter! 😐