The land is clearly covered by byelaws, so PoFa don't apply.
Just send them an email saying that, and that they have no lawful rights to pursue the registered keeper. Also, mention that they consequently are in breach of the UK GDPR rule because they asked your private data to DVLA and they keep hassling you, making the situation worse for them. You can mention you will sue them for breach of GDPR rule if they don't cancel the PCN immediately and that is causing you anxiety and frustration.
As I mentioned before if you can download a template letter here:
https://www.ninjapcn.co.uk/Just put the postcode CT214HL and choose Brockhill Country park. Just use today's date, the deadline doesn't really matter at this point as you won't go to popla.