Start by checking your bank statement and noting the charge by name, date, and amount.
Steps
Then, review the fee schedule or the product contract.
If the charge is unclear or you believe it doesn't match your agreement, contact your bank and request a written explanation or file a formal complaint about the charge and obtain a reference number.
In your complaint, specify: the charge name, its amount, the date of the charge, and why you believe it's unjustified.
Don't simply say "there are a lot of expenses"; a stronger complaint links your objection to a specific transaction and item.
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.