Deliberate attempt to hold Relieving letter even after complete notice has been served

Hi I' am working in Chennai as a Head HR in a Pvt ltd organisation. Due to personal requirement, I have discussed with my MD and submitted my email - resignation on 29th October 2022. During the discussion, I did discuss and agree with him that I shall serve the whole notice period i.e) 90 days of notice period - which is getting over on 26th January 2023 and yet i agreed him to work till 31st of January - 95 days of notice, while my employment contract is very clearly mentioned as 90 days, now the orgnanisation is insisting me to work till 31st March 2023, only then they will be processing my relieving letter etc... please help me in this case I may or may not join any company immediatley however I am quitting basically to handle my personal need - there is a divorce case that I am undergoing and I am contesting the case, I need to prioritise my Life first but my employer, having known the reason is still creating this problem What Can I do now ? pl advise Should i have right to take any legal action against them