You need to register on the Pepipoo forums and ask them there
http://forums.pepipoo.com/
You should not have identified yourself as the driver at any point btw, but they can go into more detail with you.
As an aside, it still says 7.30am on the website, have you actually spoken to the PALS team? Why on earth have they not changed it yet if they know its wrong? https://www.sheffieldchildrens.nhs.uk/patients-and-parents/parking/
Who did you actually "appeal" to?
£3 is more than enough time to park for 2 hours even in the daytime, if it got as far as a judge it would likely be laughed straight out imo. "Debt collectors" is an empty threat at this point, they arent High Court bailiffs, that can only happen after a CCJ unpaid after a period, they have as much right to enter your house and seize your property as the milkman does.