Ipad suddenly comes with activation lock

hi, my ipad 2 suddenly pop up with activation lock, i've tried to enter my correct apple id but it doesn't work. It says that my apple id cannot be used to unlock my ipad. It is very strange because i bought this ipad in new condition from 2011 and never hand it over to someone else. I've tried to erase and remove it in my icloud but still it doesn't work.