Lusitano. The police actually do listen. I was living in Al-Sadd area few months back and a similar thing happened to me. First time i called they told me to wait for some time if they dont stop i should call again. Next day same thing they didnt stop of course so i called the Sadd police station and told them that the work didnt stop. They asked for my name and mob number and requested that I wait for them near my house. 10 mins later i received a call from a policeman and saw a police patrol coming towards me. They actually stopped 2 construction sites at the same time. One in front of the building and one beside it! I was just watching from a distance after they asked me about the source of noise.
They were very supportive and understanding and told me they will not work for as long as they dont have a permit, once they obtain one they can start again and at that time it's hard to stop them.