Why wouldn't my old routers work with a new cable internet installation?

Episode 1546 (1:41:24)

Mikah from Maine
Netgear Nighthawk AC2300

Mikah left Spectrum internet service, but a recent deal they offered him got him back into the fold. The deal, however, had to include their phone service as well. He was able to continue using his own modem for the internet. He was using an older router before they arrived, but after they came, his router wouldn't work anymore. He had a brand new router, but that wouldn't work at all. He went and got a Netgear Nighthawk AC2300 router, but he's wondering why his other two routers wouldn't work.

Leo says they will record the MAC address of the router and the cable modem. In some cases, when a new MAC address is attached, they won't work with it. But since he was using that router already, they do know about that MAC address. Leo says there are ways to get it working. Shutting the whole system down, and reconnecting everything can sometimes fix it. That didn't work, though. Leo says there's no way those routers would be incompatible. This one is a bit of a mystery.