Employer forcing to complete the notice period after showing medical unfit documents of my mother and also wanting a buyout.

My company is not accepting my resignation and buy out on medical emergency of my father supported with documents. They r not even allowing me to go for buy out even I have shown the medical documents.the ceo, reporting manager no one accepting the resignation on medical grounds.They have accepted my resignation but not willing to release me in 90 days...I am.also ready to go for buy out..Even I asked verbally to release me on 15th of August and will support till date for smooth transition and rest will go for buyout but they didn't even agreed on so. Even I gave my release on Today The HR Manager told me that they will release me but they won't provide any release letter within 6 months and telling me that I cannot join any organization.They are not trusting me .If release letter not given then it is considered as a leave not release but I want to get released and also have willingness for buyout.Though I have never signed to any bond.They are saying they will not provide me my release in 3 months and will mark me red if any BGV call comes in 6 months....what can be done