I would be arranging to shower at work or a friend’s place for a while (unless you are very spartan and don’t mind a cold shower). Then I would turn off the electricity to the hot water – it is your meter, you don’t have to have hot water in your unit if you don’t want to use it. Then see what happens. It should not be many days before the water is coming through cold and the owners of the other two units try to work out what is wrong. Their electrician can identify the problem and document it for you.