locked iphone on the last owner

hello, so my iphone is locked on the last owner account and after backup i cant unlock the phone cuz is locked on the last owner account and i dont know him, or his name to speak with him to eliminate this iphone from his account, cuz i bought this iphone from amanet. Can you guys help me with this problem? Or can you give me the name from last owner to speak with him? Thank you very much! And sorry cuz i lose your time.