I have had Comcast twice in the past 3 years. I moved to a different apartment so I set up new service to take advantage of the new customer deals. When I disconnected though, Comcast said I didnt return the modem I was renting from them. Which was strange because I owned my modem. It was a huge headache and they took a week to "investigate" whether my modem belonged to me or not. Needless to say, they figured out it was mine and they dropped it. However, when I went to setup new service in my new apartment, "mysteriously" my modem no longer worked. I knew it was because they fucked with my mac address in their system but they wouldnt budge and suggested I rent a modem. So, I went out and bought a surfboard from amazon and set it up with that.
Then, I moved to Colorado a year later, and once again when I disconnected they tried to say I stole their modem. Fucking bullshit. Dont rent from them, but dont be surprised if they say the modem you own is their property.