I'm assuming you have an optical network terminal box where your fiber line comes in. From that ONT box you should have an ethernet cable going directly to the WAN input port on your router. With your old router connected, log into the router and see if you can find your WAN IP address and write it down, then release the WAN IP address, power off the old router and try connecting your new router. If that doesn't work, call your ISP and explain what you're trying to do. They will be able to release the old IP address lease if it's stuck.

With either router working, type "what's my IP" into a Google search box then compare that IP address with the WAN IP address that shows in your router's software. Are they different? If you get the new router working, delete any saved wifi connection to it from your phone. Restart your phone and reconnect to wifi.

 

Check the DHCP settings and IP address of your new router. They need to be compatible with your network. Or contact the support service of your Internet provider. They can help with the settings.

 

Thanks for the reply.
Yes, set up is as you describe with ONT box etc.
I'll give what you advised a try and update.