I was going to refuse to pay one with Australian Energy about six years ago, cause when I rang up for a disconnection and a re-connection at a new place they said it would be 2-4 weeks before either. It didn't bother me so much about the dis-connection but I needed power hooked up to my new place within the week, so I went with AGL and broke my contract with Australian Energy.
Anyway, I ignored the notices until the final notice which had a threat that if I didn't pay by 7 days they would refer my account to a collection agency and that it will affect my future credit rating. I ended up paying it cause I didn't wanna take the chance of affecting my credit and I figured that for the sake of about $100 it wasn't worth the hassle. Not sure if they would've come good with their threats or not.
Not sure if that entirely answers your question though!
