Hello Giancarlo Capanni,
Welcome to Microsoft Community.
I sympathize very much with your situation. If it were me, I would also be dissatisfied.
Most users of Surface series products may not have the technical skills to troubleshoot problems, so when they encounter a Surface that cannot be used properly, they will post their issues here. However, based on your description of the conditions of the two devices, I am currently unable to determine what has happened to these two Surfaces.
When you pressed the power button, there was no sign of these two Surfaces starting up at all? It can still be started, but you can only see the black screen?
Because if one really wants to try to troubleshoot the problem, it is necessary to first confirm whether these two Surfaces can still be operated.
If you could provide us with more information, perhaps I could guide you to try to restore them.