post resignation company calculation

Sir, I just resigned (Nov 23rd) from manager post after 15 yrs of service on medical grounds - both me and my family.For me spinal cord issue and was advised for 3 months rest in June itself. But since our Hr was behind me and bullying me with psychological irritation for last one year with spying and prying / cross checking on my every single leave I didn't asked for 3 months and took one month leave in July and even attended office on critical days. The reason for his vengeful action is since my boss (SR.VP- all 15 yrs) has put me in a assignment where the Hr brother us in charge and failed to do proper work and me did and saved close to a crore to company.Due to this my boss sacked Hr brother but the Hr saved his skin by begging top level and made him continue his role. My boss is also in July on my medical leave disturbed me with lot of assignments and advised Hr to cross check which he was already doing. On my review in August it is diagnosed that I have disc bulge / protrusion of L5-S1 and definitely need to take 3 months rest with a medical certificate failing I might end up surgery anytime on aug17th. Due to bad experiences of previous leaves I compromised treatment and continued work for 3 months by teaching all my work to my team and resigned last month end as I came to a stage where I will break down along with Hr gone to the extent of saying that he will sack me and already did the groundwork for long with groups. All for extracting money from employee after resigning for notice period. Our company never showed or been clear about their policy but claims that it is their policy in oral for everything as per their convenience. For example my appointment order on 2002 it was never mentioned of any notice period at that time.(I joined as a sportsman at that time later absorbed in administrative line on 2005). Even I was asked to resign once without any notice pay or period at 2005. Our privileged/earned accumulated leave was never encashed or credited to employees in annual year or once in 3 yrs and they keep it as 120 days only even a person has 300/400 days in real. And they never consider it while on employees exit of any and claims all unused leaves will become zero even if it is 120 days and the present policy is to serve 90 days or pay for the same provided that also they allow. Our variable pay also has lot of complications as they gave a letter on 2013 that I am eligible for 10000rs on vehicle maintenance but while claiming give only RS 2000 saying only for 4 whlr 10000. But the same when they give as conveyance by month they give for full.The same with medical too and says no carry over for any.I didn't claim medical (last year)and vehicle maintenance for last 3 yrs only can mount to RS 50000. Also I was promoted from Assistant manager to manager last year with grade change after 7 yrs which had no increase in basic whic is same for last few years but in previous periods before had slight increase when not promoted. Considering my aggravated health I put my papers after explaining everything to boss and even mentioned 15 days on my own interest only which he never asked but only behaved as such why so late.(in reality the feedback was shocking as it was he was also treating me low on purpose for years) Knowing my issue with Hr he directed me to Hr and now Hr said that I need to pay for notice period balance of 90 days in oral even I had some 30 days leave and concluded that withheld Nov salary which they didn't paid along with few working days in Dec and balance they will adjust with my unavailed medical and vehicle. My questions are 1. Even on medical grounds can a company force notice pay or work. 2.Is it not applicable for management staff leave encashment in every annual. 3.Can't unused leaves be adjusted in notice period even for 15 yrs of service. 4.when salary is calculated from 20th to 20th how can they withheld my salary and decide adjust my dues for balance. 5.my appointment letter doesn't have any mention of 3 months notice period. All they said in oral and nothing in writing. What I am supposed to do for clean exit with getting my dues and not paying anything. Pls advise