There are two possibilities for the PCN.
On is that the CEO was quick off the mark and didn't allow any grace period....
Second and IMO more likely is that the CEO saw no evidence of loading so issued a PCN.
As you were making a delivery, you should be able to provide proof of that.
I would deal with it in that respect to start with, dear sirs, I was loading, here's some proof.
Then see what comes back.