The first thing you must do, immediately, is send a Data Rectification Notice (DRN) to the G24 DPO instructing them to update their records with your (the Keeper) current address for service and to erase your old address. The highlighted words are there for a reason and you must use them.
The very first thing you should do is the above.
Some good news amongst all the misfortune - the parking company have up to 6 years from the date of each parking claim to sue for the charge. So the one issued 10/01/2019 is already time-barred, so that's at least 1 they cannot recover. Any others that reach the 6 year mark before a claim is filed will equally not be recoverable.
In that regard, it is positive that it is still at the debt recovery stage. If they want to sue, they'll need to pass the matter onto DCB Legal (similar name, same folks, but different company to DCBL), who will need to issue a Letter of Claim, and give you time to reply before filing a claim.
Let us know as soon as you get such a letter. You'll need to respond to this, but the fact they need to allow for a response allows us to delay matters slightly, which will mean that a few more of the charges will potentially become time-barred. This is obviously not a solution - but the fewer charges that are in play, the less severe the costs if the matter were to go to a hearing and you were to lose.
Can I request a photo of the vehicle entering the car park
I'm not sure what this will achieve - you seem to accept the vehicle was there.
My partner is also willing to confess she was the driver.
Don't do anything yet, but thinking aloud, this could potentially be used tactically, depending on how quick DCB Legal are in getting involved. It would potentially make your girlfriend the defendant rather than you, which I realise you may be keen to avoid, but they'd then have to follow the pre-action protocol with her too, and by the time they got to being able to issue a claim, such time may have passed that the number of charges they'd be able to claim for would be greatly reduced. I'm not suggesting taking that course of action, but it's one to bear in mind as we see how things play out.