Sometimes they get ripped open in the main sorting machine, but what they should have done is put it in a special plastic bag they have that explains this is what has more than likely happened and if anything is missing to ring the helpline.

Or another possiblity is that it could have been delivered to the wrong address (easy to do when you have to get up for work at 4 in the morning) and the people have opened it without reading the address on the front, realised it wasn’t theirs and then cowardly dropping it through your letter box rather than tell you what happened but then all the stuff should be present.