Condolences first of all.
1) On what basis do you say that the bond is one sided? In fact it is only a popular concept that the employment bond is illegal. As far as the bond satisfies the ingredients of a valid contract under provisions of the Law of Contract(Indian Contract Act, 1872) and is enforceable.
2) Further Employment agreement with the negative covenant is valid and legally enforceable if the parties agree with their free consent i.e. without force, coercion, undue influence, misrepresentation and mistake. Since an employment bond needs to be a valid contract, hence, there needs to be an offer made by an employer and acceptance of that offer by an employee.
3) The bond that you signed was for Rs.200,000/-, the term was for 2 years and you resigned from job after one year and settled to pay Rs.70,000/- for release from the bond.The fact is that if the contract is enforceable and you approach the court against the company for getting a refund of the amount paid the court will take into consideration if the company was at a loss as a result of your leaving, in terms of training imparted to you ,etc.
4) The amount you were made to pay seems reasonable proportionate to the time you spent in employment in the company.
5) You also need to consider the cost of litigation and the possibility a complete refund is remotest. Considering the entirety it is not advisable to initiate a legal action.