@eanp83 you need to make a representation, you'll have to do it by post I'm afraid and I would recommend you send it by special delivery.
All you need to say in the representation is this:
Dear Transport for London,
I challenge liability on the ground that the alleged contravention did not occur, please cancel the penalty charge.
In any event I hereby make an FOI request for the make and model of the camera device.
Yours faithfully,
Separately to that, call TFL on Monday on 0343 222 3333 and ask for the video, they will send you a DVD in the post and the PCN will be put on hold while you wait.