As per the appointment letter you must serve 3 months after submitting the notice to the organisation. As you were not having the adequate time to serve, you have to discuss with the HR Department for the buy back of notice period.
At present the bank is asking you to pay the notice pay as per the Appointment Letter. You have to pay the notice pay of 2 months and 21 days salary to the bank.
If you are failing to pay the Notice pay, obviously they can file a legal case against you.
26th May 2012 From India, Kumbakonam