Falconz: The fact of the matter is they are only maying ~$10 - $15 a month off you. Unless your prepaird to pay a higher monthly cost they cant afford to hire masses of support staff, they cant afford to call every one back.
we pay $2k a month for 10megabit national and 1megabit international to give you some comparison on costs.
It is not always the ISP at fault if there is an issue at the exchange, or the cabinet, or your home wiring its hard to track down and technical staff have a massive work load. And in alot of those cases they are relying on third party contractors at chorus or telecom to tell them whats going on.
If you call up and talk to some one about your issues make sure you get a case number and the next time you phone talk to that same person, create a relationship with them. Dont get angry and raise your voice they will be less likely to help you, treat them with respect and they will treat you with respect unless they are are jerk.
If everything fails, then find another isp that doesn't have the same issues, and change to them. They will soon get the message when their subscriber numbers start dropping. Which ironicly will mean that those who remain will have better speeds and service
Put the tail between your legs, people like you is why New Zealand customer service is so sh1t and they get away with it.