If the parking charge notice was sent to the address current at the time on your V5C, it was served correctly. It’s your fault for not updating your V5C.
Keeper liability does not apply in Scotland. In other words, as long as the driver has not been identified, the liability can not be transferred to the registered keeper. However the parking company will think that you live in England until you tell them otherwise.
You can send a Subject Access Request to the parking company to obtain all the information they hold on you, including a copy of the original parking notice. You should separately send an address update to their data protection officer requiring them to update your address for service to your current address.
DCBL are to be ignored.
DCB Legal may send you a Letter of Claim, to which you can reply along the lines of it being irrelevant for Scotland. Or they may send you the equivalent under Scottish law.
You can also ignore everything. They may eventually give up if so. Generally we don’t advise this.
But if you defend, I would do it on the basis of the registered keeper not being liable because they can not transfer the liability from the driver under Scottish law.
If you’re not going to make an effort to defend this, know that in order to do it properly will involve paperwork and empty threats. You’ll get advice here, but you’ll be responsible for handling the details.