Immediate Resignation

I joined a company with remote work at home from Surat, Company was registered in Delhi and I am working from them Surat, Gujarat. In there offer letter they haven't mentioned anywhere working remotely i don't know the reason behind it but seems tricky. I survived there around 4 and half months and there offer letter said that they can terminate any employee with in 7 days if employee not performed as per there requirement and 3 months period they need if employee wants to resign. Now I left this company on immediately basis because its offshore company providing accounting to US and working environment is really pathetic and pressure is like next level unbearable and every month they have some new policy change and due to this they have reduced my take home salary on the name of medical claim without my permission they directly reduced it, i came to know once i got the salary in my bank account. So i got fedup and left immediately, now they are threating me to recover money of 3 month notice period. So what should i do legally that they not be able to harrase me from legal notice in future ? I have there laptop with me and i am not feeling safe to give it to them without any paperwork, so can you suggest how legaly or which document should i ask from company to provide me while taking there assets back ?