It is probably because your exit gate has changed and that the information has not been displayed on the screens yet. It is also possible that many people were waiting there and that you could not see the sign that our chauffeur was handling.
Sometimes, the driver has to move the car. If so, it takes him 2 or 3 minutes.
Here is what to do:
1. stay in the terminal itself, close to the exit you used. Going all around the terminal or going out will not help at all.
2. look around you and try to find a gate number and/or a shop/café that would help us to locate you
3. try to contact the driver on his mobile phone, or alternatively on one of the phone numbers you have been given at the time we confirmed
4. alternatively, you can get some help from the Airport information desk. If not too busy, they will kindly contact us
5. once contact is established with one of our agents, this means that we will be providing service very soon