Hi Dave,
Apologies for the delay in responding to your review, we have been investigating this matter and have contacted the car park directly.
We're sorry to hear of your problems however the car park must have been able to locate your booking in order to enable you to exit without making a payment.
Comments from the car park you used are as follows: Having looked into this further, the Airparks team who own Short Run have looked on their system and can see it was received but cannot see the exact time. I note from the booking details that the booking was made the same day of travel in the early hours of the morning and the booking wasn't due to start till half four, so plenty of time for the booking to be received. But the time difference could have been that the booking came into the system after the customer arrived.
We hope that this experience wouldn't deter you from using our booking services in the future.