You have not explained clearly enough how this has all come about. If you never received a Parking Charge Notice (PCN), either as a Notice to Driver (NtD) attached to the vehicle's windscreen or by post as a notice to Keeper (NtK), what alerted you to any suspected PCN?
Was there a debt collector letter which alerted you to the PCN? If so, there should be a reference to the PCN number on the debt collector letter.
Looking at the SAR evidence provided, they have obviously failed to provide all the data they hold about you if they have not included a copy of the PCN. The evidential photos they have show the vehicle stationary for a period of 3 minutes and 6 seconds in total.
If that is all the evidence they have, together with a sign that is incapable of forming a contract, then they have nowhere to go with this except to try and scare you into paying.
At this stage, if you're sure they have not provided all the required subject data they hold for you then make a complaint to the ICO. Apart from that, you are now waiting to see if/when they issue a claim in the county court.
If/when the do, PCM will use a bulk litigator to issue the claim through the CNBC and we can provide the defence to any claim. In due course, it will either be struck out or discontinued. If it is one of the rare cases that gets to an actual hearing, most are won anyway.