How do you go about boiler maintenance?

How do you get a company in Brussels to do the mandatory check of your water boiler? This sounds like it should be a simple affair, but I'm finding it surprisingly difficult, as in Belgium appointments of any sort don't seem to be understood as binding.

Last year I asked the company that my landlord recommended, and they only showed up after three missed appointments. This year I had less patience after the first missed appointment. The Yellow Pages (Pages d'Or) list 8 companies that offer maintenance service in my neighborhood. I wrote to all of them, in French. Of the 2 that replied, neither showed up for the agreed appointments, and neither replied when I asked why they hadn't come.

So I'm running out of options but my landlord insists the boiler needs maintenance now. Any advice?