Manager is not releasing having TCS Dr. validated Medical docs

I days. I have resigned 60 days back and continuously asking to get early release. I reached out to HR for buy out option they told that it entirely depends on manager if they approve then we can release as you have valid medical docs. Now manager is gotlistenibg to me and will stretch it to 90 days . I am not sure what kind of company this isis, they don't have any sense and just want to showcase that they are manager without having any skill. Where can I give this feedback to help fellow associates from such manager?