Correct, both are connected to a separate computer in different parts of the house. I was having trouble getting Wi-Fi connection in the basement. So I put the old one down there and it worked.
Then you should be being billed for 2 accounts (in a few rare cases they allow 2 modems on an account according to some very old posts here) and that's why you are running up bits on the second modem...it's connected. I'd work on a solutions to the Wi-Fi problem (wiring isn't hard) and get one of them disconnected BEFORE they bill you.