How much time a company can take for disciplinary action?

I work in a Public Sector Undertaking Bank in India. From May 2014 I was absent from office (due to health related issues). I was not having any contact with the bank till the first week of January 2015, when I sent a letter alongwith a medical certificate. The letter detailed the reason for my absence and also I informed the bank that I am medically fit to resume duty. The bank allowed me resume office through a letter dated February 2015 (the letter gave me 7 days time to join and in the event of non compliance/ not joining, the bank reserved the option of taking disciplinary action). Due to the fact that I again had a different health issue, I wrote to the bank requesting extension of the medical leave.In the month of May I went to my branch and through formal joining letter alongwith medical certificate informed the bank that I am ready to join service. The bank has received the application but has informed me verbally that the bank is contemplating disciplinary action and till the procedure is completed I am not allowed to join service. Inspite of sending letters and email asking for written information regarding my application status (reasons for not allowing me to join) the bank has not provided me any information. The letter for rejoining service was dated 18-05-2015 and so its now one month. My question therefore is what are the legal options before me?