Being a professional developer is hard. That's why it's generally a high paying position, because you solve hard problems and are accountable for the results.
So stop making excuses. An organization of this scale should be taking serious precautions (against code errors, bad hardware, malicious attacks, network problems, compiler bugs, cosmic ray induced bit errors, etc.) when building a credit card processor.
If something truly extraordinary comes out to justify this problem, I may be sympathetic. But Occams razor suggests this was avoidable (through good process, not "I should have seen that off by one error").
I would think NASA has even more controls in place and still shit happens. All problems are avoidable in hindsight but it is inevitable that you will have problem at some point.
So stop making excuses. An organization of this scale should be taking serious precautions (against code errors, bad hardware, malicious attacks, network problems, compiler bugs, cosmic ray induced bit errors, etc.) when building a credit card processor.
If something truly extraordinary comes out to justify this problem, I may be sympathetic. But Occams razor suggests this was avoidable (through good process, not "I should have seen that off by one error").