I saw this happen at a workplace myself
They'd been over-billing customers for years, due to the way they measured the length of phone calls, essentially adding the time it'd take a call to get connected, and charging for that.
I don't know what happened about that in the end - one amusing aside was the fact the raid array hosting the old systems (which were kept running, while the company figured out what to do about said issue) was constantly failing into worse and worse state (think not only out of support, but out of manufacturing of the chips used in the thing). It eventually did fall over, costing a pretty penny to recover the data, and then a few weeks later my boss and I discovered it was STILL being run off the old system instead of the new one.
I left shortly after...