Similar thread has been started and similar queries have been raised. Should have searched different threads.
Anyway to answer your question, bonded labour is not legal in india - BONDED LABOR.
service agreement are very much valid as when you are recruited for providing service, they would be providing you some training and they would charge you the cost of training they are to or already have paid in order to train you. Apart from that there are other costs involved while recruiting i.e. opportunity cost etc. However, breaking a service bond is synonymous to paying the bond breakage charge.
You need not proceed legally having known the company that you've mentioned (actually which isn't allowed) you can always talk to the HR and negotiate or ask the consequencies of bond breakage.
Hope it helped.