You've come on here rather too late for advice if you want to preserve the discount option. You look bang-to-rights on the contravention itself, but that's not necessarily the end of the story, because there could be a 'technical' appeal based on the council management of the enforcement process. But I see nobody has yet posted anything for this aspect.
We normally advise OPs to submit some reps and let us see the response which can lead to a successful appeal due to their stupdity, but if you're not prepared to forego the discount option, then paying it now seems your best option.