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!

If you don't like it, change it. If you don't want to change it, it can't be that bad!