Sorry, but you did NOT buy a Brand New iPhone. You bought a used iPhone, which is Activation Locked. Without the actual credentials the previous owner set up the phone with, you own a useless brick you cannot use. Either return the phone for refund or recycle it responsibly as it is utterly, totally, useless to you. Apple will NOT help you remove Activation Lock on any device you can't present the original purchase receipt from Apple or an actual Apple Authorized Seller, which also shows the device serial number. A receipt from a 3rd party seller will not get any help from Apple.
Read this --> The All Too Common SAD Reality of Buying … - Apple Community