Can you be more specific eg can you tell us the airport(s) and whether these are noise or track violations. €20,000 is a hefty fine!
A quick look at the ACNUSA website would suggest that those relatively high €20K fines are mostly imposed for failure to keep within the departure VPE (Volume de Protection Environnementale) airspace (roughly equivalent to an NPR swathe) at CDG.
The French AIP, unlike its UK counterpart, actually gives the coordinates of the VPE boundaries, so given sufficiently accurate nav data from the aircraft's systems, it would be relatively easy to verify whether an alleged infringement had occurred or not.