When you applied for CAT, you might have got a registration confirmation page. Note that it's far before the exams, even. Unlike other exams, there was no need to dispatch it to the office. So, some of the students took a bit carelessness about it. But, it's needed at the time of counselling. Payment confirmation is that page generated when you're allotted to a branch in any of the allotments and you paid the fee via bank transfer..