Hyundai Sandton is ********* and they are ******

I took my car in to for service and a week after i took it there, it started shaking and wasn't idling properly. I took it back after 2 weeks and they told me the crankshaft sensor needed to be replaced. I t asked them not to do anything because I needed a second opinion. My second opinion inspected my car and told me that there was nothing wrong with the sensor, the spark plugs needed to be replaced. I was livid because replacement of spark plugs is a standard part of the service and they didn't do that. They wanted me to pay an extra R2200 for something I'm already paying for in my service plan