I always wonder about these things.
BAck in the analog days, "used" or aftermarket cable boxes were always available and would be good to go, as long as the signals weren't scrambled.
Now, in the digital age, since MAC addresses are used to activate and determine service levels, this becomes a major issue.
It seems that cable companies contract with manufacturers for custom runs with specific codes. i.e, all these runs would be sold to the cable companies who, in turn, would provide them "for rent" to their customers, and their customers only. As you found out, they are essentially bricks unless the cable company provides their blessings, which doesn't seem to happen.
So, I gotta wonder how these things appear on the "used" market in the first place?
Are they stolen, either from the manufacturer or the cable company themselves? A user is required to return tem to thecable company when terminating service or pay a stiff fine.
I'm just glad you can get your money back. That's unusual in these cases.