I wrote back to them following the advice asking if they have the authority and admin charges as per the "IGNORE" link I have just received another letter stating they do have the authority and now they want £100, Do I just send the letters back?

I did phone them and all they said was appeal again and sent me a form from PoPLA

Hi All I parked in Bristol and paid the parking fee for the hired car I had, but I gave the car reg wrong F instead of S I have the receipts and the txt message. When I came out I had a parking ticket. I appealed but County Parking say I did not follow thier Terms and conditions and now want £50....Do they have any right to ask for this I can I tell them to do one ...lol I phoned them but they were very unhelpful and just said pay up or appeal again. Cheers