"I did not notice that the sign said no stopping except 10-4pm for loading."
OK, but the sign is shown in their photos as
right by the front of your van, so difficult to make this an argument.
Nice to know you got a PCN direct, rather than getting a postal PCN derived from CCTV, which is money for old rope and shouldn't be allowed for marked bays. Having said that, your van is slightly over the double-red lines so they could have served the PCN for that alone.
What was the reason for stopping ?
And can you post the real PCN, please, we need to see it, all sides, as it may contain fatal errors