How to apply for cancelation for sale deed

My mother and my brother lived together in flat my mother taken loan to purchase that flat in the year 2004 and in the year 2009 my mother died . After her death according to policy of ICICI Lombard no need to pay the emi of flat. In 2010 i suddenly come to know that my brother sold the flat without my consent . When I ask to whom he sold he told the name of person and it was come to know that to whom he sold the property they are not giving money to him and after some days my brother was missed. I searched him everywhere but could not found .In 2019 i received i call and it is my brother crying so badly and asking for help . I brought him to my house and his condition was so bad can't explain .from so many days he had not get food for eating he was staying at footpath. he told that to whom he sold the flat they have not given any money to him and physically and mentally टॉर्चर and they force him to leave the city and also try to kill him kindly help me what can be done and how to cancel the sale deed