I think the most positive thing from the pack was the proof of postage letters and the fact one wasn't included for the appeal rejection?
(If that is a proof of postage, but that's what it seems to be to me)
I'm not sure it's of much substantive benefit, especially if (as seems possible), you have provided the wrong postcode, as there's a good chance it would not have been received either way.
I certainly wouldn't be going to court on the basis of an incorrect postcode that you accept may have been an error on your part. Additionally, the original notice says the discount is available for 14 days - it says nothing about them extending this if your appeal is unsuccessful. It seems they did this anyway, but they could argue this was a gesture of goodwill, and you've no 'right' in law to goodwill. And finally, even if you did go to court and the judge agreed the charge should be £60, by the time you'd paid the court fee and legal rep's fee it'd probably be more like £145 anyway.
Nothing you've posted so far seems to suggest much of a defence, unless there's anything helpful in the signage?