Relieving letter and Gratuity not received

I worked in an IT company for 11+ Years, due to work pressure I was not able to continue. So I informed like "Due to personal, health and family reasons" I want to relieve and submitted my resignation. Initially they didn't accepted my resignation and asked to take break and come back or even willing to provide flexible working hours. But I denied. They didn't assign anyone to get knowledge transfer from me during my notice period. As per my appointment order my notice period should be 45 to 60 days as required. Almost after a 40 days, I started asking to assign someone to take over my task. They were keep on saying, I will be relieved only if I complete some XX projects without mentioning date. I denied and told them like I worked for my notice period, I can't continue further, then after 60 days they assigned a person to take over my tasks. I extended for additional 1.5 week and transferred my work to other person. Almost I worked for around 75 days (beyond my notice period). I thought it is proper reliving, I submitted my laptop, ID cards etc. on my last working day (by Feb'22). But till not they didn't give me my relieving order even though I requested many times through mail. They are saying, my projects to be reviewed and then only reliving will be given. Can I go legal ? I got other job, so I need relieving letter urgently.