I enquired about the 'double demerits' scheme about 2 months ago for a very close friend. Mel, the deal is as follows:
If you are caught once in a 12 month period, the fine is standard, as are the points. If you are caught a second time for the SAME OFFENCE within that 12 months, the points are doubled for that particular fine. So if your first fine was 4 points. Then you are left with 8 points. Then if you are caught again within 12 months of receiving your previous fine, and the standard fine for that offence is 4 points, you are demerited 8 points. Therefore you are left with 0 points.
Sorry to hear. It sucks
Althought i'd hate to be a P Plater in NSW now! They now have the rule in place that if a P plater is caught speeding, their license is IMMEDIATELY suspended. No questions. Pretty rough, so I hope it helps reduce their road toll