Mother gave talaq now father forcing her to stay together what to do

My mother has been given talaq on last October 2015 and forced to leave our house.She took shelter in my elder sister house.After two months my father want her back and forcefully brought her and managed nikah halala for her.My mother anyhow managed her to escape from our house and again took shelter in my elder sister house in April 2016. My mother doesn't want to go back to my father anymore.So how she can get the divorce paper as there is no proof to her as talaq been done.The witness of talaq are in my father side.They are creating pressure,threaten her to be back. What can we do now?