Vw motorplan

Extending my full motorplan only for vw to tell me they can't change my spark plugs due to bad fueling , keep in mind this is the third time they are going to be changed withing 50 000 kms ,that's not usual for any relatively new car So what I'm understanding is myself and the previous owner bad fueled the car in two different cities. Having to drive a car with problematic spark plugs now , what's the use of vw motorplan then ? I ensure my car is in good condition hence the fact that one engine light flash and I immediately sent it in (preventative measures as I hate comments on a car) I have to hold on 48 hours now , I'm assuming if I drive the car and something goes wrong it'll be my problem also? Quite disappointed in vw with service I've recieved, am I going to have to have issues all the time.