Reliving letter (one side bond)

Dear Sir/Madam, Regarding employee Bond. I have Joined a reputed company in 2007 on professional contract & after completion of graduation company taken me as on roll employee dt.01.09.2014 & signed one sided bond of 03 years (36 months). Original bond amount is 1.5 lacks and completed service tenure of 2 years & 2 months. after served the company for 26 months and resigned today because of Salary Issue (Not getting timely manner) till date my 06 months salary is pending & they are not issue me a releaving letters & Experience Certificate & demanding signin bond amt Rs.1.5 lacks. Many times I requested my HR to issue me releaving letter which is must be require to join other company (Opportunity) but not getting any reply from their side. Now I come to know that bonding an employee is not legal in India and one sided service bond is null. Can you please confirm me shall I go for legal action against my company employer. Please help me… You can also write me on ajay.vaghela1977@gmail.com