Legal advise regarding Bond Penalty

Hello Sir/Madam, I have recently resigned from a Bank because of the quite stressful working Environment and my personal issues. At the time of joining, I have gone through a PO training program which provided me a PGDB diploma and charged fee for that. Also they have provided the loan for the Training Program Fee, which has to be repaid on monthly bases through deduction from the salary itself with the interest Rate @ 2.5%, while there is a clause that if I resign before completion of 3 years, I have to pay penalty @12.5% for the total principal amount for the tenure of job relationship. I have completed 1year and 9 month with the Bank and paid total principal amount. While the penal charges they are asking to pay is 90,000 which means total amount I have to pay is Rs 4, 35,000 approximately against the training fee of Rs 3,37,000.And my total earning during the last 3 years is approximately equal to the amount I have to pay. It simply means I have to pay the amount which I have earned during the tenure of employment with the Bank.It means 3 years of my life is a pure wastage, I have no earning.It is nothing but the exploitation and harrasement of the employee. Pls guide, Can I apply legally against it. And Is it worth to go legally in this matter?