Kindly remain gentle and amiable, and explain properly that you are sick and need bedrest and medical care.
Do not over react and give any chance to your bosses to exploit any mistake by you.
This is happening almost everyday in almost all the companies. Companies want to squeeze the maximum from employees.
Submit your leave application along with the copy of prescripttion (having proper diagnosis, treatment, and advice for bed rest for....days, and seal and signature of the specialist doctor) and a medical certificate advising rest thru registered post to your reporting authority. you should keep the receipt of fee paid by you, and any lab report, x-ray and report etc , and preferably signed and stamped by the doctor. All doctors and hospitals issue a medical certificate. Ask the authority who has to pass your leave to send you a copy, for your record.
if you do not get any reply, send reminder by registered post and email. Your medical and leave documents should be in order.
If you have any record that you have been made to work for 12 hours/day e.g. emails, SMS, phone calls, entries in the register with time of entry and exit from office, keep them safely. Your record should be in order.
if you are being coerced/threatened to join duty during the period you are bedridden, record the calls.
If you are not comfortable with the situation, look around an avail better opportunity in a god company with a better remuneration.
Decision of the company to terminate any employee during the period of sickness shall be bad in the eyes of law, and if the employee peruses company shall have to withdraw.