The Bank must be a private sector bank that too came into existence during the era of LPG. What is pertinent is whether your resignation was accepted subject to the condition of actually serving the notice period of one month. If so whether you obliged or simply walked out under the impression that you could pay it later if so demanded?
Any way, the Bank should not have simply terminated your services in violation of the contract of employment. Send a legal notice to the Bank.
From India, Salem