connection issues using Orbi and a Combo modern/wifi

okay folks.  i need help.   I have an Orbi RBK50 (circle with Disney) netgear router w/satellite.   I also have a modem that is an xfinity model, XFsetup -BC20....it is also a wifi.  I need to run 2 wifis becasue i have 2 gaming systems and several wireless devices in my home. (I also run a business).  my nighthawk quit (it would send a signal but not allow connection) working so i purchased the Orbi.  the orbi sends a signal but i cannot connect all of my devices. (Same as the nighthawk, which leads me to think that5 there was nothing wrong with the nighthawk in the forst place.)   the app, when i try says the the router is not found.  Now, with that said....a comcast technician just left and tested the orbi.  he says, "There is something wrong with this device, becasue I cant get internet through it."   Before I package it up and call the company for a return, I need to exhaust all possibilites of what might be the problem.  Keep in my moind.....my nighthawk and my xfinity modem/wifi combo, worked side by side for a year and a half with out conflict.....so...ideas?  suggestions.  keep your answers simple and to the point please as I will be try8ing all suggestions.    thank ou in advance.