CO2 fraud has been uncovered in the EU VAT zone[0] 1.6 billion euros skimmed by a dozen people in France. Up to 10 billion for the EU as a whole.

Unfortunately I could only find sources in french or hebrew but the amounts amassed by this operation is staggering.

[0]https://fr.m.wikipedia.org/wiki/Fraude_%C3%A0_la_TVA_sur_les...