As regards your query, please note that notice period is mandatory. Therefore it is in order to claim amount in lieu of notice period. But the matter have to be viewed as follows:
In the first instance, you have served notice on 2/2/11of your intention to leave the Bank. Therefore, 3 months notice period expired on 2/5/11. Therefore, due notice is served. The only hitch is you have left the Bank without obtaining relieving order or without putting them on notice that you are leaving the Bank after due notice period. However, there is nothing much to worry.
Since they have already accepted your resignation, payment of 2 month salary is an issue between you and your old employer. Your new employer cannot make this an issue. Your new appointment is not based on experience gained in the Bank. Therefore, your new employer may not be concerned with your relieving letter.
As far as the claim of 2 months salary, you may please inform the competent authority suitably that you have adhered to the service regulation [by giving due notice]. Therefore, they have no right to claim any amount from you.