Harassment at Job by manager

Dear Esteemed Lawyers, I am working as part of an MNC a substantial period of time. I have been toiling at work and have produced substantial business results over sustained period of time by hiring, skilling, guiding and growing people in my team at all levels. I have also delivered many large projects successfully. My manager has been methodically working to sideline me through precluding visibility on the roadmap, avoiding touch point meetings and actively micro managing to keep me actively out of action. I am concerned that this will eventually lead to quarantining me and put me out of work on performance grounds! I have appealed to my management hierarchy in writing multiple times to no avail. I am faced with stoic silence. It appears that there is an in-group and I am being actively excluded out of it. There is also an active effort to paint me as a non-collaborator. What documents should I gather methodically so that I can take legal course if I am wrongfully vilified and eventually removed. Currently I am thinking for filing a complaint in ethics helpline followed by a plea to HR. Would that suffice? What performance record should I maintain to preclude my manager to use that as an excuse as I know I am very good at my job. Thanks in advance