It's a pay at the machine upon exit which I did, the PCN was for parking in a unmarked bay.

Hi I apparently recieved a PCN from Gemini Parking Solutions for parking in an unmarked bay at the London Aqautics Center at the Olympic Park on 27 Feb 2015. There were no prominent signs for parking or penalties in the car park. I was unaware of the PCN till I received a Reminder Notice letter on 28 April 2015 posted to my home address as the registered keeper of the vehicle for a charge of £100 now from £60 if paid within 14 days of the PCN. Stupidly before coming onto this site I appealed to Gemini Parking Solutions supplying my details stating that I was the driver. The PCN was not on my windscreen when I returned to the car it must have blown away as it's quite windy at the center with no buildings nearby. I appealed that I never received a PCN, obviously they rejected my appeal and sent me a image of the PCN on my windscreen (to my surprise!!!) and they claimed that their parking operative noted that the driver ripped up the PCN in front of him!!! - that never happened. They have now sent me a POPLA Appeal form, what should I do now. How should I appeal ? Thank you.