No. It was nothing to do with the conversion rate. It was the fact that 99% of the clicks were clearly fraud.
When half the clicks are from sites with 100% CTRs, it's pretty certain they're fraud. I gave them the chance to refund on the frauded clicks, and just the ones that weren't certain fraud. If they'd done that, I'd have been happy to pay the amount owed (even though I didn't get a single conversion). However, when you deny obvious fraud on your network, and charge for it, you are no better than the people performing the clickfraud. I refuse to give my money to fraudsters.