I am outside of the UK until August so I'm worried that if I appeal, I would miss any further correspondence and potentially miss new payment deadlines if the appeal isn't accepted.
Please give the dates of your trip.
Apart from paying, you can submit representations within the discount period, to Westminster who will inevitably reject your reps. They then normally re-offer the discount, or the option of registering an appeal at London Tribunals. A period of 14 days will be allowed to pay the discount, but I'm not sure how long you get to either pay, (the full amount) or register an appeal at LT.
From what I can see, you might manage it by submitting your reps towards the end of the discount period. They then have to reply which could be a week or a month, one never knows. They have only erected a single sign, with nothing in the carriageway to indicate a left turn. The scaffolding and "hut" looks to have totally obscured their single sign.