My mother once had a "we tried to deliver ... come and get it tomorrow" card from Royal Mail. The next day, along she went ... "sorry, we can't find it. Do you know what it looks like?"

It never turned up; we never identified what it was supposed to be, or who sent it, making contacting the sender impossible.

CityLink are particularly bad. I had to collect my printer from Glenrothes (quite a trek from Perth!) - fortunately, as it happened, my mother was working in Glenrothes at the time, so she collected ... a laptop. Yes, they gave a laptop to completely the wrong person, by mistake. On the bright side, they suddenly became much more cooperative about delivering the printer once they needed to get the laptop back...