Issues after receiving new router, phone line stays in use.

We recently noticed that XFinity was recommending that it was time to replace our router with a newer one. We received the newer one a few days ago. After setting up the new router, the internet and TV are working fine but we are now having phone issues. The new router they sent is a Cisco DPC3941T. The old one was an ARRIS TG1682G.

The phone light on the router is solid, and the phones answering machines ‘line in use’ light is off. As soon as we make or receive a call, after hanging up the phone, the light on the router remains blinking and the ‘line in use’ light on the answering machine remains blinking. When the line is actually being used the phone light on the router blinks constantly, when it is in this “broken” state, the light blinks twice, stays solid for a second and then repeats. At this point if someone tries to call us they are getting either a busy signal or an instant hang up. The router is also making a faint clicking sound. 

If we unplug the phone line from the router, the clicking stops. After plugging it back in things go back to normal, but after 1 call the problem reappears.

Please advise if this is an issue with our phones/answering machine or an issue with the new router.

If it is the router, is this something that XFinity can fix remotely or have we possibly received a defective router? We have not returned our old one yet, so if we need to revert back to that one and return the new one we can.

Note: We have already tried restarting the router and resetting the phones.