as a postie got to say that the majority of the people i work with try their best, at this time of year you can imagine it is very busy.
as for not redelivering an item i know that when mail volumes are high we would rather get an attempted delivery on every item rather than re-delivering items. you can have item put for collection in a local post office for a small fee.
we have heard that they are working out a way of having a locker drop system, where items are delivered to a 24 hour location i.e. supermarket, where the customer can collect whenever.
finally as in all occupations you will get the odd bad apple.
if you want to complain, don’t phone, put it in writting :D