I deal with iinet through my business for phone and internet, rural area so all Telstra infrastructure. I've always had fairly prompt service when it comes to fault rectification.
I think the key is to to be reasonable, polite and friendly, but straightforward and no nonsense as to your expectations.
First and foremost, write shit down,, time date details of conversation and who you spoke with, Take note of their name, if you don't catch it, have them repeat it, and call them by their name in the conversation, the idea is to instil in them some kind of responsibility, but also to make them want to resolve your issue. Don't get angry, don't be rude, be personable, but also be firm.
Remember always the merkin on the other end of the line is a person, and if you treat them poorly you alienate them and their natural reaction will be f**k you, next. They likely deal with dumb merkins on the line all day, and if you act like all the other dumb merkins, they'll treat you exactly the same as they would all the other dumb merkins.