Related to releaving from current organisation

Hi I am working in a startup and I am serving a notice period and 3 days are remaining they are asking to extend the notice period, Also denying an experience letter and relieving letter. The reason they are saying the company takes action against one candidate who has been involved in beating someone and after that company has terminated that person reason they are giving for extend Notice period is until the full and final process has not completed that person who has terminated you cannot leave the company and you have to extend the notice period and I am the person beaten by that person. I have logged the complaint to the company and they have taken the action against that person. after that we mutually resolved the problem after giving an apology letter. also after terminated that person hr didn't inform me related to extension of notice period when 7 days remaining that time hr inform me this. I have to join another company ASAP . When this incident happened I am already service notice period. Please suggest me.