Hyundai wonderboom excuses

I took my Hyundai venue Motion TGDI automatic today to Hyundai wonderboom. The car lost power and it jerks when accelerating, with engine light on the cluster. It has 54000km now and undergone all services from starting from 15000km. Their diagnosis says it needs spark plugs but they can only replace them when it reaches 60000km. It has fully paid warranty booster for 7years, service plan and maintenance plan. Now I'm told to pay R1200 since it hasn't reached 60000km. I'm so disappointed with Hyundai wonderboom. I took my car without fixing I'm waiting for it to stuck.