First, submit your complaint to the bank itself through an official channel: the call center, branch, website, email, or any other complaint channel the bank provides.
Steps
Request that it be registered as a formal complaint, not just an inquiry.
The bank must provide you with a reference number immediately or within a maximum of two business days.
In normal cases, a response is expected within 15 business days.
Keep the reference number, responses, and supporting documents.
If the bank does not respond within this timeframe, or if you dispute the response and exhaust all available channels, you can escalate the matter to the Central Bank according to the published regulations.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.