If the neighbouring OC is refusing to deal with your OC then perhaps your OC should consider taking independent action. See here for a detailed list of options and processes to go through:
https://www.legalanswers.sl.nsw.gov.au/guides/neighbours/trees.html
NCAT may not be the most appropriate path for you to take. An extract from the above link states: The Trees (Disputes Between Neighbours) Act 2006, called the ‘Trees Act’, provides a much cheaper and simpler method for resolving some of the tree disputes between neighbours than the legal remedy that was previously available.
A Court Order from the Land and Environment Court may be required. The steps to achieving that Order are contained within the above link and also the Land and Environment link here: