Mental harassment and workplace politics

Hi, I am working in an organization from last 1 years and 4 months. and from last 6 months I am getting harassed, mentally by my Function Head. There is some conflict is going on between my reporting manager and his team and boss. And because of that conflict the head started imposing unfair conditions in front of me. He shouts on me without any mistake of mine in front of other colleagues anD never Took my points on the same. Associates in the organisation are free to come and go on Saturday's as per their work requirements and even if there is no work they need not to come to the office. But 2 days back the head made this a compulsion for me that I have be there in office on Saturday at 9:15 am. He pointed me out with wrong words in front of 5-6 others employees in the lift. He checked my phone which is not right. And many more incidents are there. When he is around I feel insecure. I have discussed the same with HR of the organization but she took his side only saying that it will not be intentional. I don't want to work anymore in the organisation but also want to tell him that he is doing wrong with his subordinates. Please suggest what should I do!