New modem problems

Hello,

I recently got a non Xfinity modem (Motorola MB7621), which says it's compatable with Xfinity. I hooked it up, and after an hour long chat with Amit in customer service, it was activated on my account. I'm trying to set up a router I got as well (TP-Link AC1900) and even though I get internet through the ethernet cable into my computer, it isn't working for the router. And to make matters worse, I'm only getting about half the speed I should be, and when I go on the website, it says my modem isn't communicating. When I try to troubleshoot, it only references my old modem. The cherry on top is, every time I try to get in a chat for help, the "chat unexpectedly closed". This is a problem because Amit had to remove the Xfinity router from my account, so that doens't work anymore, and I require the wifi for my job. Any help would be greatly appreciated.