Williams Hunt PE Ripped me off

I bought an Astra Turbo from the mentioned company two years back. I paid R14 000 for a maintenance plan ontop of my service plan. The salesman told me that the vehicle is covered for everything I.e all minor services. Basicaly the only expence would be petrol and to change the tyres. Now they are billing me for something as minor as having the oil changed. Would I have paid that kind of money if I knew this? No. People should be warned against Williams Hunt PE