You are obviously confused by all this legalese and pontifications. My advice is as follows:
Ignore everything. Forget about appealing. The only way this PCN is going to be resolved will be when a county court claim for debt is issued to you. We can provide a suitable defence if/when the time comes.
A claim is easily defended with our assistance. No amount of appealing will ever get an Excel/VCS PCN cancelled.
What you need to be aware of, for now, is that any debt collector letters or reminders can be safely ignored. The debt collectors are powerless and rely on the recipients gullibility and ignorance to scare the into paying the now inflated (by a fake £70) charge.
Never, ever communicate with a debt collector. They cannot do anything except scare you. Now that you are aware of that fact, you can safely ignore them.