Holiday Extras Parking Reservation Fail

I booked a parking place for my upcoming trip to Edinburgh with Holiday Extras last week. The parking lot was completely filled when I got there, which was 2.5 hours before my flight. I had no problems using this parking lot in the past, and it was only a 15-minute shuttle ride from the airport. I did a full three-circle search of the region in the hours leading up to my flight, but came up empty-handed. Due to the lack of an attendant, I began to feel a bit anxious. Unfortunately, I had to leave my car at the airport parking, where I paid almost twice as much, because I couldn't find a spot. I would like my money back for the service that was useless to me.