If the iCloud account is from a previous owner, then you'll need to contact them and ask them if they have any other Apple device in use that they used the ***same*** account with, they can then 'remove' the device in question via their account (linked devices). If you are unable to contact them then [link|https://www.youtube.com/watch?v=ar37ye4gdOs|this video will explain the situation and show the only real known solution.]