Ignition plugs change only after mileage or even after time

Hello, my XCeed will soon be 5 years old and has approx. 28000 km on the clock. My seller has unfortunately been terminated and now I have to go to another. I have now got an appointment with the other dealer and according to my documents only an oil change service is provided after 5 years. In my question about the costs I was called about 400 Euro. On my request why so expensive with an oil change I was told it also the spark plugs after 60 months have to be changed independently from the running performance. In my operating instructions only after 75,000 km. Has something changed there? Kia wrote that what to do is in my documents. Can it be that it is dependent on the year of construction? Kia itself really is no help. I don’t want to pay for my warranty but also not useless things.