I telephoned an operator and booked our two family cars in to the short stay car park for one week, and paid for both cars on my card. On our return my daughter had no problems exiting with her car, but when I tried the barrier would not lift. I pressed the help button and spoke to a security man who said my car was only booked in for one day and I was to return to the pay machine and pay the shortfall before he would lift the barrier. I refused and went to the barrier office for a "discussion", where eventually he accepted that there had been an admin error and let me go without further payment. Despite an early flight arrival this incident caused me to be very late for a pre-arranged function that night.