5ghz wifi disapeared/not showing, help!

Hi Alexandre

did you try to reboot the modem?

Check if you disabled here

This change can also be applied through the Wi-Fi modem user interface:
1. Log in at: 192.168.0.1 from the web browser of any device.
2. Log in using the following information:
Username: cusadmin
Password: xxxxxxxx (Password you chose during initial setup)
3. Go to the next section to apply changes:
Wireless → General Settings → 5GHz

You can also try a factory reset


Using a thin, pointed object, hold the restart button on the Wi-Fi modem for 10+ seconds. 
 
Once your modem has restarted, follow the same instructions as when you first installed it. 
 
IMPORTANT: this operation will reset any changes that have been made to the settings of your Wi-Fi modem to date. You may also have to reconfigure the Wi-Fi settings of your devices (network name, password, etc. .) 
 
The default username of your Wi-Fi network, as well as the corresponding password, are written on a sticker affixed to the back of your Wi-Fi modem (Default Wi-Fi network and Default key).

You can also contact customer support by chat

1- Click on this link: https://fizz.ca/en/faq/none-my-devices-can-access-internet-wi-fi-or-using-cable-how-do-i-fix-it
2- The green chat bubble with the ? should appear after a few seconds in the bottom right corner.
3- Click on it, and select chat if available, or any other option

Mike gave some very helpful tips.
Try to reboot the modem and check the admin settings of the modem.