@Dannyboy71, welcome to the forum. Please stop panicking over this. If you follow the advice you won't be paying a penny to these scammers.
Before we proceed with the necessary advice, please tell us whether the Parking Charge Notice (PCN) you received was a windscreen Notice to Driver (NtD) or a postal Notice to Keeper (NtK)? Which unregulated private parking company has issued this PCN?
As for the previous posters question about the address on your V5C is because it is often the case that when someone changes address, they update their drivers licence details with the DVLA but are unaware or forget to update their V5C address separately. The parking operator will only send the PCN to the address on the V5C but a debt recovery company will do a simple credit reference check to obtain a current address, which is why the first you know about this PCN is when you receive the debt recovery letter.
You can safely ignore any and all debt recovery letters. Debt collectors are powerless to do anything, no matter how threatening their letters may seem. All they can do is try and persuade the low-hanging fruit on the gullible tree to pay up out of ignorance and fear.
Never, ever enter into any communication with a peerless debt collector. Ignore them.
For now, wended to see the PCN you received. Only redact your personal info and the PCN reference number. Leave everything else visible, especially all dates and times. We also need to know what you wrote to the parking company. This is important because you may have made some mistakes by contacting them before receiving advice. However, that does not mean that it is fatal to your case.
Invariably, if you follow our advice, these cases will reach litigation but will eventually be struck out or discontinued.