OK so you went next door prepared to negotiate, you were kind and polite, you were the model neighbour, a true diplomat and what you got in return was an arrogant, self-interested, dismissive, defensive and hostile response. You did you best to be reasonable and they just weren’t interested in you side of the story, they accused you of being the problem, and you left feeling angry and frustrated, you got dismissed or bullied - yep you have got the Neighbour From Hell and now is the time start Keeping a Diary - make your first entry about what just happened i.e. what you did and said and what they did and said in return the time, the date etc.
Do not be tempted to write forthright, abusive, indignant letters to NFH about how rude, careless and stupid they are, if you do have to send written communication over something like the boundary fence state only what is necessary, date, description etc., enclose the relevant material like fence quotes and copy of the fencing act for their information, do not make personal reference’s or threats. If you consider it appropriate to make a complaint to your NFH in writing have a look at the NFH in Britain site Template Document Index they have a well worded template letter that can be tailored to suit your needs. When you post a letter like a fencing notice it is a good idea to send it by registered mail this avoids any dispute later about it not being received - keep a copy of what you have sent and the receipt for the postage. If you have an overwhelming need to write a personal letter to the NFH telling them what you think and feel get a lawyer to look at it before you post it.
You can find a copy of a fencing notice for NSW here.