Bought a used iphone

I recently purchased a used iphone from a store on the internet. Mercari. Here it is icloud locked through apparently another person. I tried to ask the person that I purchased the phone from about this. And once purchase is complete u can no longer speak message this person. So I sent email to apple it's self. I sent the receipt that I got from Mercari when purchasing this phone. Well that's not good enough they want the original owner name when and where they purchased it. So again no where no where with my old iPhone that was stolen no where with another phone I purchased. Why can't apole tell me or get hold of the original owner of rhis iPhone that is icloud locked. I mean it was reported lost or stolen. I would think that apple it's self would contact the owner of this ohone to tell them it was recovered but no thet want information i can't get for them. What's the point of having all that info for a lost or stolen phone if u nor apple cant let this person no their phone has been found.