Bad customer service

Marius has done lots of good work for us in the past and we've had a good professional relationship. But the last few times I've asked him to work, he says he'll come and he doesn't. This has been going on for about a year. We have urgent work and he promises to come and then just doesn't arrive. We phone and he doesn't answer. Why promise to come work, on numerous occasions, and just not pitch up?