You will only succeed under CPR 13.2 if the claim form was incorrectly served. That doesn’t appear to be the case if it was sent to the ‘correct’ address, being the address recorded by the DVLA on the date of the contravention.
CPR 13.3 requires you to show that you have a viable defence that ought to be tried, or there is some other good reason for a trial. So you need to put forward as many good defence points as you can, ideally by submitting a draft defence, which the court could order to be entered if it grants your application. There seems little point in rehearsing the defence in a witness statement when it can just be exhibited in a draft defence.
The witness statement should really concentrate on why no acknowledgment of service or defence was filed in time, i.e. why did you not comply with the rules? It can also give evidence as to why you have a good defence and ought to be able to ventilate it.
