CM400 and Xfinity No Internet with Ethernet or WIFI

Hello internet,

You can consider me a complete novice at setting up my own internet, but I am pretty tech savvy and can learn quickly. Just please use laymans terms...

I bought a CM400 modem and TP-LINK AC1200 Router to use inplace of paying Xfinity's ridiculous equipment rental fees. I just moved to a new place and am trying to set up my internet for the first time on new equipment.

Backstory: I had previously bought an ARRIS modem which had trouble connecting as well... after being on the phone with Xfinity for an hour and them sending over a tech, they said the problem was the modem was not compatible, thus the CM400.

Now trying to set up the CM400... when I connect the modem to my MAC book pro 2011 (10.11.6), I see in network preferences that the Ethernet is connected, but I have no internet access. Wifi is the same... I am connected to the router but no internet access. I was on the phone with Xfinity for another hour and they could not do anything and they suggested I call Netgear. I did that as well and waiting for them to call me back this morning... which did not happen and I will be out of the house for the rest of the day. I was reading another thread on here suggesting to disconnect the modem from the cable outlet and waiting 20 mins, which I'll do when I'm out for work. If I come back and it doesn't resolve the problem, any suggestions?