Extremely poor service from Nissan Ladymsith

My vehicle went in for a 150k service to Nissan Ladysmith. this service entailed draining the radiator fluid, less than a month later the bottom radiator pipe which was s****ing against the air-conditioner pully got worn through and all my coolant was lost, fortunately the fluid drained happened after I got home. Nissan claims it is not their fault, yet they were the last people to work on the vehicle, it is also very clear that this hose cannot be positioned almost against the air-conditioner pulley. I drove 150 000 km without incident yet after NIssan worked on the radiator to change the coolant as per their Job Card I now have a problem. I phoned them numerous times, each time they say they will phone back but never do. I please need help in order to contact the right person within Nissan Group