Ant Problem (What is happening here?)

I’m studying and living in Germany and recently I noticed there was a swarm of ants around the corners of my apartment. I contacted my work that is working alongside the landlords to see if anything could be done but..

I noticed they are making these little hills of dust around the walls. This wasn’t here yesterday night before I slept, so I was wondering what exactly is happening here. Ignore the yellow shape, that’s a sticky trap for plants I am using as a small trap for the ants.