Not interested in reminders or debt collector letters. The only document that is relevant is the original Notice to Keeper (NtK).
Under no circumstances reveal who was driving. You are only communicating as the Registered Keeper. They have no idea who the driver is unless you tell them. You are under no legal obligation to identify the driver to an unregulated private parking company.
The first thing you need to do is send a Data Rectification Notice to the DPO at ECP instructing them to change your address for service to your current Scottish address and for them to
erase your old address. If your V5C is now updated, you can send them a copy of that as your proof of address. If not, just send a utility bill with your current Scottish address on it.
If you believe that any data we hold may be inaccurate, incomplete or out of date then you can contact us via email at DPO@eurocarparks.com
Once that is done, you can ignore everything else from ECP or their debt collectors. There is no Keeper liability in Scotland, for now. They will not pursue a claim under the simple procedure in the Scottish courts. It is just not worth their while.
Eventually, they will give up. However, you must get them to update their records and to erase your old address.