Advice.
Before posting in a forum such as this, make the effort to find the appropriate subforum (this is clearly a "Private Parking Ticket" case), find the cunningly hidden "READ THIS FIRST" sticky at the top of that forum - which gives you basic initial advice and indicates what information we need to be able to offer meaningful advice, and post appropriately in that forum.
N.B. This thread has now been moved to the correct forum. Do NOT start a new thread for this case.
The most obvious gaping whole in your account of events is that it went from the odd random letter to the Directions Questionnaire form N180. To all intents and purposes, your defence to this claim is the defence that you must have lodged, but neglected to mention. This cannot be amended without the permission of the court.
Without seeing your defence, there is no point trying to give meaningful advice regarding defending the claim.