Dissappointment and need help on how to solve this case

I took my car to nissan the Glen on the 18 December for a full service as I was going home in the eastern cape but after they did service on my car it over heated and stop 2 hours from my home now they are telling me stories and it went there before service as a precotion on my side but my crying now bcs whn I checked it looks like it has never been touched as the engine is still diety u touch were the supposedly changed plugs.