Welcome to FTLA.
Can you please show us the back of the notice?
As issues at their end mean they have not delivered the notice to you as the registered keeper within 14 days, they can only pursue the driver - they don't know who that is (unless you tell them), so, as the keeper only, you can appeal along the lines of the below (NB - if you are
not the registered keeper, if it's a lease/hire vehicle for example, then let us know as the appeal will be different):
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 seeking 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,
If appealing online, be careful there are no drop down/tick boxes that cause you to identify who was driving, and keep a close eye on your spam folder for their response. If they do not respond within 28 days, chase them.