Go thru the information published by your own bank, e.g;
2. The bank will safeguard, securely and confidentially, any information that the customers share with the Bank. The bank will continue to maintain its tradition of not sharing the transaction information in customers’ account with any one except when required by law or statutory agencies.
4. The bank will give access to customer information to only those employees who are authorized to handle the customer information. Employees who violate Bank’s Privacy Promise will be subject to the Bank’s normal disciplinary process.
5. The bank will not reveal customer information to any external organization unless the bank has previously informed the customer in disclosures or agreements have been authorised by the customer or as required by the law and statutory authorities.
Relate with BCSBI Cods, IBA , RBI guidelines….
Your lawyer may arrange to ask OP in court from whom and how IT obtained the statement of account that belongs to you and not OP.
You can ask your bank who passed/shared the copy of account statement and why and on what grounds and by which clause of any agreement signed with you or consent by you?