I purchased a modem from someone on craigslist to use for my new cable internet service. The modem appeared to be unused and in brand new condition. However, the sticker on the box with the modem's serial number and MAC address was removed.
I first tried using the internet a few hours after the technician activated the service. I immediately noticed my download speeds were slow. Running a speed test, I see that my download speeds are less than 1Mbps (my service level is for 50 Mbps). My upload speed seems to be fine.
My guess is that some previous owner of the modem has used the serial number and MAC address to clone my modem. When I activated my internet service, they were able to be provisioned on the network under my account. Now they are downloading massive amounts and using up all of my allocated bandwidth. Is this feasible? If this is true, is there anything I can do?