When you file a formal complaint with the bank, you must obtain a reference number to track your complaint.
Key points
If you don't receive it immediately, the bank must provide it to you within a maximum of two business days.
Keep the reference number and the date of your complaint.
Just because you contacted customer service doesn't mean you've registered a complaint; make sure your complaint has actually been registered.
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.