It's crazy enough this will be fixed soon.
Years ago I found an actual hidden error in my bill. (This was early 2010s). The system was calculating the EC2 reservation savings incorrectly for some of my servers. I was crunching all their detailed usage data on a regular basis in an 18 tab spreadsheet and couldn't get it to fully reconcile. I spent months trying to track down the discrepancy. Once I found it, I had to convince AWS their system was wrong, which took another big chunk of time. Meanwhile the discrepancy continued to accumulate.
After 14 months I got a $7,000 refund. I was told it had to be approved by the head of AWS. I've never seen a calculation error on their part since.