After going through your complete case and all the responses, very first thing I would like to say that you must not take any action in bewilderment or rush or without considering the situation and also must not be careless with the things in life that you did here.
Well now can you please share your Appointment Letter provided by your present employer?
See it doesn’t matter what company policy they have or not, the terms defined under an appointment letter can definitely help you. Your appointment letter with present employer is really important because both the Employers are talking about “Company Policies”, therefore, I would like to know what terms of employment used in it in this regard. Also i would like to know if it is any clause in appointment letters that treat it a violation of company rule and you can be terminate if found with this kind of situation or previous dismissal, if yes, could be a problem for you. Although, I accept that company policies are above to all but they cannot so easily deny or overrule the terms defined in your employment letter (Present Employer)
In addition, I request you to clarify the following points
-You got admission with Barathidasan Institute of Management in 2009 and took leave for your studies, so it means you were working with XXX at that time and allowed to continue your study and join them back until 20 July 2011?
-you granted "Leave Without Pay" on a mutual request/understanding or had any written permission from XXX?
-Plesae share if you have documentation in this regard and also your offer/appointment letter with XXX
-You informed them that you were not able to join them back, it is accepted,but have you ever resigned?
(I guess you never resigned because you were busy in study and lately realized when you found dismissal letter and started looking for solution)
-And, if you resigned, do you have any correspondence with them in this regard?
-You said that XXX decline your request to grant you more "Leave Without Pay", do you have any correspondences in this regard, if yes please share.
And
-When you joined your present employer?
-When, what, how and why you disclose your previous dismissal to them?
-What exactly your present HR people are saying, and the current development in this case.
-If you still have not resigned from your current position, I suggest you to please do not do so and let them take the action whatever they want
Your Mistakes:
-Your biggest mistake that you were unprofessional and too honest.
(Yes, still there is a value of Honesty, Sincerity in our Society but one must not forget that our society where we are living is a developing world where the things, culture, perception, ideology and everything are undergoing many changes. One needs to be more professional and wise with every action in this regard)
-Second, you allowed both the employer to talk to each other, was your another big mistake that you were not supposed to do.
Please furnish the details. Also i request you to please compile all these details and your case as in a "Case Study" with a word format that will certainly help you and other with many things in future.