Parking Eye - Crown Wharf Shopping Park, Walsall

Went shopping while visiting family for the weekend and parked here. Originally missed all the signs but after 30mins we paid with loose change for 2hrs parking. As time started running out we paid for another 2hrs, being asked to enter the number plate both times. In the end, we paid for 4hrs and parked for just under that.

Two weeks later, I received a "fine" (what I now realise is an invoice) for £50, increasing to £80 or then £110 if I failed to pay up within adequate time.

Initially, I wrote to the to appeal (as I thought this was the appropriate term based on the guidance on the back of the invoice). I stated when and where I paid for the parking and that I had paid with loose change so had no proof of purchase. I hadn't kept the tickets from the machine and stated the thought that I should do was unreasonable. I requested that they review CCTV footage from the car park to witness me paying for my parking and asked that they checked in case I mis-keyed my number plate into the pay machine, (although I doubted that even I would do this twice). I did however, provide receipts of my purchase in the shops there and offered further proof of shopping at Crown Wharf.

I finally received a letter stating that my appeal was unsuccessful but I am galled to pay when I legitimately paid for parking at the time! However, I have no proof of purchase and although the advice seems to be "don't respond" and don't use the term "appeal", I've done both of these things and now wonder where I stand if I refuse to pay?