Poor customer service

Poor srvice delivery from call centre consultants. I took my car in for service at VW Strydom Randburg and it came back with an EPC problem. Apparently a spark plug isn't connected properly and it is causing misfire and my car engine vibrates when I accelerate. I called V but they said my service for 165000KM doesn't cover that and it that they didn't do anything to the spark plugs, but my car was fine before then. I called MFC since I'm their client and pay them for a service plan and they said it is not their problem I should talk to the VW. VW is telling me I should call MFC.. so it is a back and forth and my car suffers in the meantime. Called again and the agent kept me on hold till my airtime depleted. Why are we paying for a service plan that covers everything when we can't even call for basic spark plugs?