Have you tried connecting the Hisense TV to the 2.4 Ghz Wi-Fi SSID or is it trying to connect to the 5 GHz SSID? The 2.4 Ghz is a stronger signal and may have been used in the previous modem.
If it worked with your previous modem using the 2.4Ghz band SSID, it should reconnect to that same frequency band - have you changed the Wi-Fi Name in the TV Network settings to match your new modem ? The Hisense TV may not support the 5Ghz band and depending on distance from the modem, the 5Ghz may not reach the TV. Also does the F@ST 5366TN have both Wi-Fi Bands, the 2.4 Ghz and the 5.0 Ghz Enabled and visible to all Wi-Fi devices.
Hi - I am sorry that I am not familiar with the F@ST 5366TN menu structure and default settings. I thought I had read a previous forum post stating this new model's two SSIDs were broadcast at the same time. If that is the case, you should see two of them when you connect any wireless device to the modem provided your Mobile Phone, Notepad or PC supports Wi-Fi 802.11ac for the 5Ghz connection. On the previous F@ST 3864V3HP model, it would display the two bands , something like e.g. OPTUS_AABBCC for the 2.4 Ghz SSID and OPTUS_AABBCC_5.0Ghz for the 5 Ghz SSID.
In the event of the display name for the F@ST 5366TN 2.4Ghz SSID being different to your previous modem, you should be able to verify what SSID the TV is currently connecting to in the TV Network Settings. In case it helps, can you reprogram your TV Network settings again within the Hisense Menu structure with the new modem's 2.4 Ghz SSID name and password and Save settings if applicable to see if it then links to the modem successfully. Maybe turn TV OFF for 30 seconds and then ON again.
Generally you can view the modem settings by typing the IP address 192.168.0.1 (verify by looking at the sticker label on the modem in case the number is different) into the top input bar of your web browser. You will be challenged for a User Name and Password - these again should be on the sticker label.