danih – The neighbouring property is definitely responsible for the damage caused by the roots of their tree.
Are there any other large trees that are in the vicinity that could also be adding to your problem? Your neighbour will look to avoid the responsibility of the root damage as much as possible and will likely blame other trees – so be prepared.
To fully prepare for any future action you will need to obtain some more information ……
1. Ask the plumber to provide a written report about the damage caused to your pipes from the neighbouring tree.
2. Take photos of the tree.
3. Obtain a screen shot copy of a Google map satellite image of your property and its immediate surrounds which show the fig tree.
4. Obtain a quote (preferably two quotes) for the costs of all of the works involved e.g. trenching, replacement of the pipe, back filling and replacing the car park surface.
The steps to be taken after you have obtained those pieces of information are outlined in the link below:
https://www.matthewsfolbigg.com.au/news/local-government/trees-disputes-neighbours-nsw/
And in The Trees Act is linked here:
https://www.legislation.nsw.gov.au/inforce/def76566-c66f-4d9c-cc90-bf028ed0ca59/2006-126.pdf