I want to share with you a pretty nasty case that happened to my CPA camp which turned a green camp running for 2 days into red in less then an hour
As you know with the CPA camps you pay fixed price per conversion, so every time my tracker fires back the postback, i get charged by the source
All was going nicely until I noticed the spike in conversions, when I checked in the networks dashboard I see that traffic started being redirected to a smartlink, which was converting like crazy with a super low payout.
But guess what?? I still pay the sam fixed price for those sales to the traffic source!
This just totally crashed my camp and the whole camp got into red
I contacted my aff manager to see whats the issue, probably the offer was capped which was not mentioned in the description
Sure, things like this happen.
When you run CPA campaigns you should also always redirect not targeted traffic to somewhere else.
For example imagine you run a higher payout offer in Tier1 Geo and you pay $10 per conversion.
Now a part of the traffic is from India and you receive several conversions with $0.05 each but still you pay $10 per conversion.
This sucks, I can feel your pain.
Those rules that @twinaxe mentioned could probably save your back, make sure to implement them next time.
Anyway, mistakes happen in media buying to all of us, let it be a good lesson for the future 
Have had this happen to me many times lol, that's the risk of running CPA buys. As said before, good idea to set pixels at the offer level not globally. Also not a bad idea to set up a monitoring script that can pause your campaign if it notices the offer has capped (if you have API access for example to your traffic source).
I've coded my own script to do this so I don't have to babysit caps all the time and because network emails are usually delayed or get spamboxed.
Did you try to talk to the traffic source? Since this was a non-standard situation, they could show some understanding and issue a refund .. no idea who the source is, just making a suggestion to think about.