How to file complaint against bank for disclosing customer details

Hello Couple of days back I have received an email from ICICI Bank mentioning about revision of home loan interest rates and they attached a pdf file to this email. This pdf was password protected. In first page I could see my address and loan details etc. When I scrolled down I could see letters of 46 customers in file. I was shocked to see Bank is disclosing customer details like this. Just like I received 46 other customer details, my details might have shared with other customers through the email. When I contacted customer care they replied that due to technical error. However its shocking for me how a bank can disclose customer confidential information. How do we trust their banking system now. I would like to know what kind of action can be taken on bank for their negligence and breach of customer confidential agreement. Please advise me on this.