Missing parcel

Lock***5 Good day

I sent a parcel on the 20th November, 3 packages split into 2 lockers. The one locker Lock***0 was delivered and collected , a single parcel. On the 24th November Lock***5 was received as a single package, what happened to the second package that was placed in the same locker.

I strangely received a call during the week from the courier guy asking if they should still deliver the package, that it was marked do not deliver ? I don’t understand what this meant ? In essence there is one one pack missing from the parcels I shipped, the receiver only received 2 packages of the 3 I sent. The app also shows a parcel is still in transit ? This is also confusing , I just want to track my missing package.