If a bank has shared your account number with a third party without your consent, you have several options. You can lodge a complaint with the consumer forum and the Reserve Bank of India (RBI), especially if you've suffered financial losses. While sharing an account number itself might not be an offence, sharing details like balance, passwords, or transaction history is. It's advisable to formally notify the bank in writing that your information should not be shared. The bank might also take action if you post defamatory messages about them online, though they often avoid this. Consider switching banks if you're unhappy with their service.