Does Comcast/Xfinity sabotage the used modem market?

I'm at the end of my rope with this company. I have purchased FOUR (4) modems used in the last few days. Each time, I had to reboot my modem before the 800 number would allow me to talk to a human being to add the MAC address of the modem to my account. So 20 minutes of useless time go by, THEN i can simply hand over my MAC address. BUT, apparently Comcast customer service is region locked? So if someone sells a modem from another "district", customer service claims to be powerless to remove the modem and switch it to my account. Except, now they WERE able to do exactly that for my new Netgear 1150v modem, but the service cuts out after 3-4 hours and I have to reboot my modem. Comcast claims there is no issue, and Netgear claims they can't do anything because the modem is sitll on someone else's account. Does Comcast intentionally make it a nightmare to get off their rental hardware? It must be this way, there is no other explanation for the dumpster fire that has been my modem switch.