Nobody opens the door for the heating service. The contractor drives off, comes a second time, and the second call-out is on the invoice. That is the obvious part, and it is the smaller one.
The second visit is not the only item
With a meter reading on a deadline, whoever does not open gets estimated. The estimate goes into the service charge statement, the statement arrives months later, and then the complaint arrives. The work on that lands with the manager, not with the meter reader.
On top come the calls: when is he coming again, do I have to be there, can I leave a key. Each one is small, and they all arrive at the same desk.
Why the announcement so often does not land
Because it comes too early and is then no longer visible. A notice two weeks before the appointment is read and forgotten; the day before it hangs behind two newer sheets. And when the date moves, which it often does, the announcement is wrong rather than missing.
The letterbox has the same problem in a sharper form: paper disappears among the advertising, and nobody sends a second letter for a one-day shift.
What changes
The appointment is where everyone passes daily, and it stays there until the appointment. Moving it is a change in the browser and visible in the building a few minutes later, with nobody driving out.
This does not solve every missed appointment. Whoever is away for a week still misses it. It solves the cases where someone was there and simply did not know, and that is the larger part.