I feel ripped

Good day I bought a Ford Fiesta ambiente 1.4 2017 in May 2018 and I took it for service sometime around July 2018 with the kilos of around 19263 then the same day after the service the car gave me some issues and i called the dealership to book it and they booked it , I then took it and they checked it and they told me the issue is the battery, the lady (Belinda) advised that they can change it, its gonna cost me R3000, she then told me that because I've already serviced the car for 20km am not covered under that warranty. I then went to buy a new battery myself, When i did my research i only got to find out that am still within the warranty.