Early release by salary in lieu option

Hi , I have asked my manager for early release due to certain health condition of my mother. She is 68 and staying all alone. I have asked my manager to release me and he has informed me verbally on my LWD that is 30th April 21, now he is coming back and saying management is not agreeing for early release and i have asked him what about buy out option. He is denying saying management is not agreeing at all. But it has mentioned very clearly in my Offer letter that either i can serve 3 month Notice period or can go with salary in lieu options. Just to note i have no dependency on the project and it seems from my project including me 4 have dropped down there paper. My questions are: 1) Why cant i get the buyout options when it is mentioned very clearly on the offer? if 90 days NP can be taken seriously then why not this. 2)If something goes other way around and i am not getting early release and based on Humanitarian ground what legal action can i take against it? 3) What Impact it is going to put if I have take a harsh stand against it?