I had the same thing happen to my family. We moved and took our boxes with us back in 2004. Apparently the csr who told us we could take the boxes across town with us decided not to note it on the account. Well we had to fight with them to get the charges reversed. I forget how but we finally got them reversed.
Don't know anyone who would be seriously telling customers they're allowed to move with Comcast equipment to another residence be it across town or across the country. The customer rep was wrong in saying it can be done and the charges were legit. Sorry.