Thanks all, I've found the problem it was my ISP router that was blocking it. --> solved.

Thanks @InnerScientist@lemmy.world & @ark3@lemmy.dbzer0.com

Actually I don't think it's the firewall, because all the other programs, protocol are working fine. I've tried with chrony too but I get

No suitable source for synchronisation

May be because the client is a VM ?

Thanks @cypherpunks@lemmy.ml But I rather want something that run locally.

Thanks @HelloRoot@lemy.lol But I stop with raspberry pi..

But I found https://wammu.eu/python-gammu/ I just have to foud out if it could work with a USB-GSM-Modem, dongle and it should do the trick.