One resident in our building has filled the miklot with his personal items (and half of the stairwell going down to the miklot). We asked him nicely to empty the miklot and we wrote a letter signed by most of the other residents, but to no avail. He even paid the fine that was imposed on him, but the miklot is still full. Can we take him to Beis Din? What can Beis Din do to enforce their decision?
You should go to a Bais Din. There are different things that Bais Din can do to encourage the person to remove his belongings from the miklat, such as a “tzav meniah”, which is a command that prohibits him from keeping his belongings there. This is what can be done as a start.