Booked well in advance and paid extra to park in the short stay car park for 1 week. On returning and inserting the ticket to the exit barrier, it would not let us exit and had a message that the exit date had expired, which was not the case. Tried pressing the button on the machine for help, no response, tried several times, still no response. By this time frustrated drivers behind us had to reverse and go round us to another barrier. In the end we had to reverse up the exit road and re park and walk over to the customer service office at the long stay car park to have them verify our ticket so that we could exit. When I asked the attendant why no one had responded to our help call she just said that they had someone else being difficult at another machine! However there were 2 attendees in the office at the time. She also had no explanation as to why our ticket had not let us exit the car park as expected. So very poor customer service experience and we may as well have paid less and parked in the Long Stay as we had to walk over there and back anyway to sort the problem out.