Chosen Delivery Time Ignored

What is the point of allowing customers to choose a delivery timeslot if it is not honoured?

I was contacted via WhatsApp and asked to select a delivery time. I chose the 12:00–14:00 slot and took half a day’s leave to ensure I would be home. Despite this, the courier arrived at 9:00am while I was not there.

I have now been told the delivery was unsuccessful and that I need to reschedule for next week. This means taking time off work again for an issue that was entirely avoidable. This is extremely frustrating and unacceptable service.