Breach Of Service Agreement With Employer

I am under a service agreement within my organization.it was said that for the job the training has been provided for 6 months and hence I have to stay in company for 3 years. But the training provided was just 15 days and I completed 2 years and resigned due to horrible working conditions. Now they are asking to pay bond amount and when I countered them saying I never got 6 months training they said it is on job training not mentioned as such in the agreement. Please help is it legal Thanks.