If your complaint is about loan fraud, you can file an online police complaint through the CCTNS Citizen portal of the state police or the National Cybercrime Reporting Portal.
If the bank is registered, you can also lodge a complaint with the bank directly. You can further file a complaint with the Banking Ombudsman of the Reserve Bank of India.
For more help, please clarify the nature of the bank loan. Is it a financial fraud or a dispute with the registered bank?