Just a lost neutral, not that horrific.
That was exactly what happened, but... Who cut the neutral? And why?
In addition, why the electric company took longer than 5 hours to react (cutting off the supply)?
I got in touch through their emergency number, to alert about the problem, as soon I noticed what was happening. And the operator did not believe me!
Well, it might be reasonable, maybe they have many calls from trolls, but later I learned that many of my neighbors also called warning of the problem.
So... Lesson learned! After that, I added under/over voltage and surge protection to the electrical installation.
Unfortunately when the electrical installation was made these protections wasn't mandatory, so nobody installed one.