Perhaps you could provide the model of your modem/routern as well as the plan you're currently on? fibre/cable?
where are the cable installed?
which cable is to the lan port and which cable is to the Internet port?
did you try doing and direct ONT connection to see if able to surf internet?
Fibre termination point -----> Fibre Modem ------> Computer
CATV point ------> Cable modem -------> Computer