Still trying to understand your setup and I should have determined early on what modem and router you have. If in fact, as Marius surmises, you have an all-in-one "Gateway" (Modem + Router + Wi-Fi) from your ISP, what is the purpose and function of adding the Netgear router?
You shouldn't have both components acting as DHCP Servers, NAT (Network Address Translation) and Firewall, or you will run into problems.
If the reason for adding the Netgear router was for better WiFi coverage, you have two options:
Option 1: Use the ISP gateway as a Modem only in Transparent Bridge Mode and use the Netgear router for all other functions - Routing, DHCP Server, Wired LAN Connections, WiFi Access Point and Firewall.
Option 2: Use the Netgear router as a Wi-Fi Access Point only by disabling its DHCP Server and NAT functions and use the ISP Gateway for Routing, DHCP Server, Wired LAN Connections and Firewall.
Steve