Consumer action law Centre. They give some of the legal background to why the payment notices are unenforceable and confirm that it will not affect your credit rating. Their approach is to take it to the Victorian Civil and Administrative Tribunal (VCAT). My opinion is that this is way too much effort and is not necessary.
Parking Fine Appeals – Care Park. Lots of useful info about Care Park. It analyses their signs and their payment demands.
The Age: Private car park ‘fine’ notices may be unlawful. Article detailing some of the controversy. Note that (as is typical of a lot of the internet), people are careful to use words like “may” and “might”, because they fear getting into legal trouble. It is a pity so many people are so afraid of the law.
Consumer Affairs Victoria took a private car park operator to court. The court declared that the operators had engaged in misleading or deceptive conduct in a number of ways.