You were engaged in commercial delivery work so were engaged in loading, but all the CEO saw was a locked private car. The bay is not restricted to goods vehicles, so your parking there was legitimate. They have rejected because they always do, knowing that >95% of people then just cough-up; is this you ?
Problem is that to take the matter further you must forego the discount option, and wait for the Notice to Owner and submit your reps again, but with our help with the final text. NtOs are sent by post to the name and address on the V5C Registration Certificate.Are you the owner and if so, are the V5C details correct and up-to-date ?