Going in Windows Task Manager > WiFi, i noticed i was connected using 802.11g despite both my laptop (Dell Inspiron 5547) and my Orange Livebox supports 802.11n.
I logged in 192.168.1.1. Tried to set the WiFi to 802.11n only.
But it wouldn’t allow me to.
I went on changing the encryption for my SSID.
And i got connected to WiFI 802.11n 😀