Stop fretting about the kangaroo court decision of the IAS. They are a corrupt and mendacious part of the IPC, the very same ATA that the parking operator is a member of.
That rejection is clear evidence of how dishonest the IAS assessors are. Besides falsely claiming to be legally trained to solicitor level or higher, it is clear that this lying toad would fit in to a North Koran court system. They are NOT legally trained and tht is why their decisions are anonymous and unsigned.
Here is a graphic that show why the IPC and the IAS are judge, jury and executioner, all in one. Ignore their decision.

The decision is not binding on you and you do to pay anything.
All this means is that now you will start to receive useless debt recovery letters which you can safely ignore. Debt collectors are powerless because they are not a party to the the contract allegedly breached by the driver. All they can do is try and intimidate the low-hanging fruit on the gullible tree into paying out of ignorance and fear.
Come back if/when you receive a Letter of Claim (LoC) that gives you 30 days to pay. Ignore everything else that comes from a useless debt collector.