What should I do if technicians failed to show up

Dear community members,
I signed a contract about a month ago, but my internet still hasn't been activated.

I wasn't at home the first time so the landlord helped wait for the technicians. But I got a message like this that day:
"Lieber o2 Kunde, wie uns die Telekom soeben mitgeteilt hat konnte die heutige Schaltung Ihres o2 DSL-Anschlusses durch den Techniker nicht wie vereinbart erfolgen. Wir werden Sie im Laufe des Tages anrufen um schnellstmöglich einen neuen Freischalttermin mit Ihnen zu vereinbaren. Ihr o2 Team"
Was there a problem about the building or the technicians didn't show up?

I called them once I came back to Germany and O2 quickly scheduled another visit. But, no one showed up at the scheduled time.

I called them again and, quickly another visit was scheduled for next week.

I mean I respect the efficiency of scheduling visits, but I am a bit worried that it will be the same and I have to wait for them the whole morning next week.

Is there a way that I can check why the first time things didn't work and why the second time no one showed up.

Is this because of my address? It is quite central in the city where I live. It should be easy to find, right?

For the last two times, I attached a paper on the door saying that they ring the bell and someone is here for them, or they can call a number.

Is there a way I can make sure technicians will come? If they won't come the third time, should I just schedule the fourth time or the fifth until one day they come? What else can I do?

Best,
A poor guy in Frankfurt