The employees and company have an obligation not to exploit this even if the issue is only discovered after the fact.
You don't get to export any of the responsibility to your customer. They don't prepare the bill and it's not their job to find your fuck ups
I once got a monthly water bill for ~$35,000 at a residential, single-family home. Good thing I was paying attention and looked at the bill before the auto-pay bank draft hit.
Someone had misread the meter.