Is deputation contract legal?

Dear Sir/Madam, I have query regarding "Bonded Labour in Software Company". I was working in a Software company based in Pune for almost 11 Years. I have resigned the company in June 2014 on medical grounds & served for 3 months Notice period as per company policy. Sept 2014 was my relieving day. On the relieving day when I went to HR room to collect the Relieving letter and Experience letter, they informed me that I need to pay approximately 5 Lakh. The relieving letter and experience letter will be issued only after paying this huge amount. When I asked why I have to Pay this amount, they informed me that "it is a basic salary for the remaining 12 months which I have not served after coming back from deputation". After coming back from deputation I have served the company for 1 Year(12 months) Background of Deputation and Contract policy: I was deputed to Other country for a project development(Not for Training) for 1 year(i.e from Oct 2012 to Oct 2013). Before going on deputation, they had asked me to put signature on Deputation Contract letter, which stated that after coming back from deputation I have to serve for 2 Years, If I fail to then I have to pay the Basic salary for the remaining months. From January 2013, for all employee's going on deputation the Deputation contract was changed i.e after coming back from deputation employee has to serve only 6 months as per company policy.(Note: during this policy change, I was still on Deputation to other country) When I checked with HR, why the Policies are not same for all employee's, they say "the policy was changed in January 2013 so you don't come under this policy" For Example, - a employee who goes on deputation in December 2012 has to serve for company till December 2015 - a employee who goes on deputation in January 2013 has to serve for company till June 2014 In My Offer letter it is mentioned only 3 months has to be served after resignation. Now I am not able to enter into the company as 30th September 2014 was my last day in the company. They have not given my Relieving letter & Experience Letter. Question 1: Is this kind of Deputation contract is legal? Question 2: Can a company have policies which is not same to all employee's? The 6 months policy should have been applicable for me too right? Question 3: Since I had given Medical reasons, is still the Deputation contract legal? Question 4: Can I ask for the reason through RTI? I sincerely request you all to suggest me as early as possible. Thank you in advance,