If you are able to use the online form for appeals, I would recommend doing that. Whilst you shouldn't have to, pragmatically it at least means your appeal has been registered.
If you cannot operate the online form, I would be happy to submit it on your behalf with your permission, but you would need to share with me via private message an unredacted copy of the PCN including your personal details, so I would understand if you were not comfortable doing so.
You could also escalate a complaint to the BPA about Britannia's failure to adhere to the Code of Practice, but our first priority is to get them to consider your appeal.
Using your insurance to determine who can drive the vehicle is simply nonsense. My insurance would cover me to drive your car if I had your permission to do so, for example.