Holden Commodore 2010: Engine problems

I reported a grinding noise from the engine in my 2010 Commodore SV6 ute at 24,000km in April 2011, again at 37,000km in August 2011, and again at 46,000km in June 2012. All these times coincided with a service and although I reported it as an engine grinding noise, they told me it was heat protection plates that could have been the cause and were taken off and reworked and noise went away, but not once did they listen to me as I protested they were wrong. In December 2012, at 55,351km, the engine seized. The dealer agreed that it had an issue and told me they would replace under warranty with a long motor. It was, but I have since had ongoing issues with the new motor. There was misfiring, said to be because the intake manifold was carboned up, warning lights have come on, and it used oil. They then said they would replace the motor with a short motor. It turned out that they had only fitted a short motor the first time, not the long motor they claimed they'd fitted. I protested and put in a claim for a replacement or heavily subsidised replacement vehicle based on the fact that they still can't tell me what is wrong with the car. Holden came back to me with an offer to trade my vehicle in on a new one and they would pay the on-road costs. No consideration was given and the point was missed that I bought a vehicle that hasn't performed to a satisfactory standard since first reported noise in April 2010 and has had a major failure by way of seized first motor? I brought in the Department of Fair Trading and they went back to Holden with my findings that I could better anything they offered by walking in off the street? In January, I returned after 4200km to have the oil consumption looked at and reported to Holden TAC. They informed me it only used 1.1 litres, but I questioned the result as there was hardly a reading on the dipstick? Currently I am waiting for their findings to see their next move. I am little fish being screwed by big fish, and don't know what to do anymore.