I'd say it's an inside job, or there's a skimmer installed on an ATM or gas pump, etc., that you are using regularly. Not sure if you already did so, but I'd switch banks and change all places where I use the card, and start using cash at those places which I can't change (convenient gas station, etc). I've been lucky; only had it happen once where it actually went through (a fake $1100 charge from a used brick dealer in Jersey City), and that was traced back to a waitress with a skimmer at TGI Friday's in Woodland Hills, CA, who disappeared in the kitchen with my card for a few minutes mysteriously. The other times it happened, the bank caught it first and didn't let it go through, and canceled my card to give me a new one. Those times, they said it was random account number generators at work.
Charles