They have. Each and every year.
It's sad that such a central trope from the 'Leave' campaign turns out to be an outright lie, but there you go. I suspect it's because grunting 'KIPpers cannot tell the difference between "material error", around 4.8% (which is lower than the USA's 5% but well over the UK's 1%) and "the auditors not signing off the accounts". But 5% of the money goes missing doesn't make for an easy soundbite, because just 5% going missing sounds like a pretty good job, for a government.
The EU spends its money in places where corruption is rife, and the institutions of Government are weak, like Romania or France, not in places with strong institutions like the UK or Germany. And the European union funds are going into especially corrupt sectors like construction. Perhaps this error rate is understandable. Building roads and airports in Romania is going to help the Romanians, and eventually us. Just as the Marshall plan rebuilt Europe after the Second World War, and gave the USA a rich continent to trade with, rather than a poor continent which needs supporting in a little over a decade, Western Europe should have been MORE generous to the East when the wall came down.
Had Russia been treated after the Cold war like (west) Germany had post 1945, then perhaps Russia would not now be having its tantrum, and threatening to nuke everybody.
So, the closer you look at the arguments being deployed by the 'Leave' side, the worse they get.
- The cost? Non-EU Norway pays 90% of our fees per head for access to the single market (which we want, right...?), UK's EU dues are falling.
- Democracy? The belief the EU rules the UK is overblown fantasy. The UK remains a democracy, in the EU or out. The EU spends 5% or so of UK managed expenditure, and shovels a lot of high-volume, low impact trade law to us much of which we'd implement even if we were out. This really isn't a big deal.
- We'd be free to trade? I think this is the weakest argument of the lot: The EU's trade deal with India was scuppered by, urm.... the UK, citing immigration concerns. You think we could do better alone? Australia and NZ would welcome us back with open arms? Possibly, but they both see the USA as far more important. The USA is ridiculously protectionist, despite which, the EU might get TTIP through. I doubt the UK could do much better. The EU isn't hampering our trade with the USA or Australia. And in any case, the EU is THE champion of free trade in Global fora, mainly because of British influence.
- We'd control our borders? Well most of our immigrants currently come from outside the EU (mainly the Indian subcontinent), where we do in fact have control. I doubt much would change here. In any case the immigration of hard-working polish plumbers is less of a problem to most people than 'KIPpers imagine.
- We don't want to be part of a superstate? And we're not. The Eurozone may become one, but the non-Euro countries will not be part of it.