This is very common even in nice neighborhood. People can lose their income, or they inherited the apartment and never have much in their bank account. You are lucky you have only one, sometimes there are few in the building. Everyone has to pay more and take that one to court. One day, after 2-3 year maybe, they will find the money to pay. It's probably very hard to foreclose the apt in Argentina. The sad news is that, after a few years,
they finally pay the due, but peso is already worth lot less. They probably can negotiate with the court and just pay the principal. There is not much you can do. My next door has not paid for a long time, the people in the building are mad, but they pretend nothing happens when they see the family which does not pay, pretty civilized I think. I always brought gifts to the kids next door, they cant pay the expense, and it was their mother's apartment, I found them to be very nice people. They probably feel the pressure but do not have the means to take care of the problem.