Please post up the letter, redacting yr name & address.
I cannot see why they need further evidence as your opening post seems convincing.
However, can you get a photo with a 3/4 image of your own car similar to the angle (if not from the same height!) as the 4th photo in yr opening post.
This link will lead you to images of a merc - select one(s) that indicate the distictive size window shape of the Merc in the video.
Also you could edit the number plate photos with arrows to highlight the differences.
That you car was
x miles away is irrelevant - the point is that it is clearly not the vehicle captured by the TfL camera.
It ;looks as if they are trying to tick boxes to justify accepting your reps.
See what others say and post your draft submission here before sending in.
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EDIT - crossed with Stamfordman's post: make sure you included is point about Y/V.