I recently got dinged for leaving my credit card "in the drawer". The "credit utilization" component of my rating according to creditkarma.com went from A to C

I recently got dinged for leaving my credit card "in the drawer". The "credit utilization" component of my rating according to creditkarma.com went from A to C because my utilization was 0% (I pay for everything with my Simple debit card or direct debit). 0% is in the C bucket, while 1-20% is in the A bucket. I started using it like that. I use it for some of my purchases every month, and have them debit the full balance at the end of each month. My rating in that category went back to A the very next month.