[Connectivity] Zoom 5341 and Netgeat Nighthawk router issue

Hi, I'm in the process of moving my internet service from ATT to Comcast. I use a Netgear Nighthawk router behind the modem. It works great on Uverse but will not work on Comcast. I can however direct connect the PC to the Zoom modem and I can connect, but not when I'm using the router. I've tried calling Comcast TS and they are giving me the run around saying things like it's your modem, PC and router - *sigh* I see the Zoom runs on 192.168.100.1 and have tried to change the WAN IP address to match the 192.168.100.x with a sub-net of 255.255.255.0 and still no luck. Any suggestions on what might be happening? Thank you in advance.