That's such a small thing tho. It was a tiny amount and presumably they would've refunded it had it gone through. It's also possible they would've discovered it themselves soon enough, since many companies only look at the money books at the end of the month.

Also, I doubt you'd get a "reasonable explanation" from any other company - at best they'll say "sorry it was a (human|software) error, we've taken steps to ensure it won't happen again", as disclosing anything more is usually against company policy.