I copied-and-pasted my comment from another post.
"You don't rent a standalone modem. You purchase it.
If Cox comes to your house to initially install your Internet service, they'll charge your bill for a modem. You can rent a router from Cox (Panoramic), which includes an Internet and phone modem, but that'd be the only time you'd rent one...that is, to partially rent one.
Cox has a list of "certified" modems for their network.
https://www.cox.com/residential/support/cox-certified-cable-modems.html
You don't have to purchase an Internet modem from Cox. You can buy it anywhere you want. Just ensure it's on the list of approved modems.
Also, don't buy somebody's used modem because Cox has them identified, logged, archived...or something...I don't know. I read a post about a subscriber trying to activate a used modem but Cox wouldn't do it. I think they just want to sell modems."
https://forums.cox.com/forum_home/internet_forum/f/internet-forum/21562/upgrading-modem
