Problem after cable modem change

Yesterday, I installed and activated a new cable modem to accomodate the higher speed service that I now have. Everything went smoothly. However since I installed the new cable modem, when I try to access Live TV under Xfinity Stream from my home network, I get the message to connect to my home WIFI. I am connected to my home WIFI when I get the message. I suspect that the problem is that Xfnity is not recognizing that I am connected at home because of the new cable modem. I called Customer service and they were of no help. Does anyone know how to fix the issue or how to contact a knowledgeable tech support person who will be able to fix the issue for me.