Not seen any reports previously with that speaker, personally speaking. I take it you didn’t choose to get the extended warranty cover? What troubleshooting steps were tried with Sonos Support? 
Maybe sell it for spares/repair, or if there are reputable repairers near where you reside, perhaps explore that option.

Battery or charger failure are possibilities.

The speaker never turned on again. The support team told me to run tests and nothing. They told me that in the system the speaker appeared "off line" and that it would no longer be useful.

The speaker never turned on again. The support team told me to run tests and nothing. They told me that in the system the speaker appeared "off line" and that it would no longer be useful.

Did you not remove and test the li-ion battery as outlined here? It is replaceable if it shows as faulty.

https://support.sonos.com/en-us/article/replace-the-battery-in-your-sonos-move

I followed all the support recommendations and had no results

Today I requested to be seen by a supervisor, and after 3 hours I could only get the case signed to someone who will contact me within 48 hours. Almost 2 months without being able to solve a problem. Terrible after-sales assistance

I read somewhere that they are replacing the ONEs due to battery failure, but from my experience with this it must be very difficult. If someone faced something similar, please contact me and guide me.

I am writing from Chile, by the way.

If you mean the Sonos One speaker (gen1/gen2) there’s no battery in that speaker?… I’ve seen one or two people report that they replaced their Move battery - I think it likely needs replacing after say 3 or 4 years anyway, if perhaps used heavily and constantly charged/discharged … and of course, li-ion batteries can become faulty if left discharged for long periods. Have you not tested the battery - it might just need replacing, perhaps? Maybe checkout the various videos on YouTube.

The battery worked perfectly and for the expected hours (4-5 ) but the speaker stopped working one day and never turned on again. Support told me that it would not work again as the system did not detect any faults.

I did find this link too…

https://zontsound.com/fix-sonos-move-2-not-charging/

..but personally I’d just perhaps remove and test the battery and then go from there.