why wont recovery mode reset my iphone in itunes

My grandson had a iphone 6 Plus which he used for over a year. He then got a new phone and gave me the 6 plus. He wiped it clean in the right way, find my phone was turned off. He removed the device from itunes. I was going to use the phone but has touch disease so I hit it on the palm of my hand and seems to be working. Tried to set it up but after hitting on my hand, it on activation lock and wants a icloud.com account that he has never had. what can we do? Only proof of purchase is invoice from ebay without showing serial number. I am lost as to what to do.