Cancellation of Car deal

Bad customer service, no compassion, lack of interest in what I complain about, unwillingness to assist. I bought a Demo car from MMG Kia Newcastle and the car was delivered to me without any inspection . On my inspection I found lots of faults on the car and when I confront them the manager denied all that I was showing her of which the nearest dealership confirmed it on the inspection. I am stuck now I want cancellation of the deal and the don't wanna came to a mutual agreement. I returned their car as I don't want it and the bank says they cannot do anything since it has to come e in writing between me and the dealership of which they are refusing to do. I don't know what else to do.