Not getting the salary

I started working for the organisation in November and worked there for a month. I was supposed to get the salary on the 7th December which i did not get it. I fell sick on the 5th December and i asked my management to credit the salary so that i can get the medical examinations done and get the proper medication on time. i submitted the medical documents for the same. Till 13th they did not and i had to go to the office (still sick) to talk about it and then they told me that they will give me half now and half later when i rejoin the work. My condition was even worse after that and i got chicken pox, all the documents and pictures were submitted for the same. Now its 4th January (recovering from chicken pox) and they are asking me either to resign, for which they will deduct 15 days salary or start working and they will credit the salary in February including January's salary. But i need the salary for my medical and living expenses, which they are liable to pay. What can i do in this situation