Not sticking to 'all day' appointments

I was informed by Telkom that they will install a phone line for me at my personal residence and I must be available as this is an 'all day appointment'. I didn't have anyone available to help and I was desperate so I took a day's leave, just so that I was available for the rest appointment. I phoned Telkom's call centre on the day before the appointment to confirm that it was indeed booked. I waited the entire day and they did not arrive or notify me that they were not going to be able to keep to their appointment. Why does Telkom schedule an appointment that they cannot keep, and then don't inform us? I feel upset because the customer's time is clearly not a concern of theirs.