Travel lane's last disappointment

We booked a cruise through Travel Lane. Ivonne was very efficient throughout but she spoiled everything through an invoice error that we used when booking for a flight. She said that our arrival date was 12 March instead of 11 March. That mistake was R500,00. She changed flights for us and demanded that we pay an extra R500,00. She never even bothered to apologize for her mistake.. Why did she charge us a booking fee for her mistake?