If they want to rely on the provisions of Schedule 4 of the Protection of Freedoms Act (2012) to hold you liable as the registered keeper of the vehicle, they must
deliver the notice within 14 days. They have failed to do so. You can therefore appeal along the lines of the below, as the keeper only:
Dear Sirs,
I have received your Parking Charge Notice (Ref: ________) for vehicle registration mark ____ ___, in which you allege that the driver has incurred a parking charge. I note from your correspondence that you are not able to hold me liable as the registered keeper, under Schedule 4 of the Protection of Freedoms Act 2012 ("The Act"). You have failed to issue a Notice to Keeper in accordance with The Act, and it is now too late for you to do so.
There is no obligation for me to name the driver and I will not be doing so. I am therefore unable to help you further with this matter, and look forward to your confirmation that the charge has been cancelled. If you choose to decline this appeal, you must issue a POPLA code.
Yours,
Separately, their notice wrongly implies that they can pursue you as the keeper - this is a breach of the Private Parking Sector Single Code of Practice. You may wish to complain to NCP (and subsequently the British Parking Association) about this misleading conduct.