I had had similar problems with my credit card for a couple of big purchases, but I am completely understand and even loving of that system due to FRAUD

Someone in vancouver duped my card and was buying small things, 50-10$ purchases. But then he tried to buy $3000 worth of jewelry and it was rejected, thankfully, otherwise i would have had to pay until the bank agreed it was fraud (they still owe me $250, this happened in september).