1. They can not demand Rs.3 lakhs for your leaving before the Bond period,
2. They can claim the salary they have paid you during the period,
3. Keeping original educational certificate by the employer has no legal sanction and it amounts to illegal arm twisting,
4. Ask back the said certificate ( they may claim that they never had it) and lodge a police complaint if they refuse to return it,
5. Now, if you are sure that you will be able to get a fresh job without collecting the release letter, then yu can leave the company as they will certainly not give you a clean release letter,
6. Indian Laws are not employee friendly. So, act judiciously duly weighing your strength and weakness.