I guess the issue is what was the correct line - where the new fence is, where the old fence was or somewhere in between?

If the old fence has was in the wrong spot but had been there for 25 or 30 years then under adverse possession you might be able to claim that becomes the new title line. I believer on the law institute of Victoria website there is a guide to fencing disputes.

Before I got a survey done I would be looking at my own title and getting one of those really long tape measures and trying to work out if they have taken land or if the last fence was in the wrong spot. If you use a tent peg to hold to tape in place you should be able to get a pretty good measurement. If you think they have taken your land I would then speak to the council about it they might be able to help. Or speak to the department of infrastructure, who should hold the latest land survey for you to get a copy of. I would be complaining about it though, not just because it is 10cm x whatever length your property is but if you want to build you might have to pay to get a new survey done & then change your title etc.