ICloud Unlock: iPhone 6?

I bought a used iPhone 6, and the previous owner forgot her Apple account and has no proof of purchase.

Has anyone managed to unlock an iPhone, and if so can you please explain how?

Maybe restart the whole thing? Just write down people's numbers. I hate to do it too about a month ago

Nothing you can do about it. You are out of luck.

Restore it via iTunes on a pc.

I've done it with a phone my niece had and also with an iPad

Open ITunes, connect the USB to the PC, then while holding down the home key, connect the phone to the cable, then follow the prompts. It works on all generations of iPhone, iPad and iPod

Totally impossible, it's the basic "anti theft" system.

Even a full reflash of the operating system does not unlink it from Apple's database, only the real user login can do that.

To be blunt it is stolen and you will get in trouble if caught with it, ever!
Get your money back.

You can't. You unfortunately may have been scammed if that's the case.