I find it very hard to believe that Google would change your AdWords settings without you knowing it. So, I do believe that you mistakenly changed the numbers yourself. I guess this can happen; it's an honest mistake.
Another possibility would be that someone else got access to your account. I'm sure Google has access logs. They must have some type of records documenting the changes in your AdWords campaigns. Did you have any AdWords consultant or an employee managing PPC campaigns for you? Anybody else who could have gotten your password?
But if you are so sure about not having done anything wrong and that the error is on GOOG's side, I'd say go to your credit card company and try to get the money back. Talk to your lawyer, too. Not sure how the members of this forum can help you out with this...