Somebody somewhere doesn't like me

The company that I work for licenses out software for other companies to use so that they can send sales through to us using simple software, thus eradicating the need to call us and send us the information.

We spend many hours creating documentation for the people who install this software on the client machines. We also run training courses on how to install this software on the client machines.

So why is it then, that there are some (though I need to stress, not the majority) people who don't listen in the training course and then don't read the infopacks that we send to them, and think it to be perfectly acceptable to get to the installation and call us to walk them through it step by step?

This really gets my goat and takes up a lot of my time, time that could be spent on the many other far more important things that I have to do in a day.