Failure to fix oil leakage while car is on motor plan

I took a car(Ford Focus 2014 model) for a service to Ford Centurion on the 29 September 2017. The lady who registered my car is Marilette. She phoned to inform me that my car has an oil leakage and that I need to pay R1400 for Ford to fix it. I told her i wont pay that money as the car is still on warranty. She then said that the reason for me to pay is because I brought the car late for the previous service. As per the service book, I disagree with her explanation because i am allowed to bring the car for service on the set date and/or when the car had reached 40 000km. My car had not reached 40 000 km.