Now Speedtest.net works.
The contract of my ISP provides: download max = 20Mbps, upload max = 1Mbps.
This is the current situation:
The ISP says that it needs 10 days to stabilize these values but these days they have not changed.
if on Monday, Aug. 10 they will not be significantly increased, I will start to send this situation to as many sites as possible!
[A clarification: the contract is totally devoid of information; those 20Mpbs were in the advertising of the ISP!
Moreover, it is not clear why, if the voice contract is valid, they require you to send a signed copy of the contract they sent by email!]
Note: I have no hardware (line) problems; I obtained 16.5Mbps -0.89Mpbps from my previous ISP