Fighting it? Well, you know my feelings about the way Dish does a lot of things. But, a deal's a deal. You agreed to subscribe for 12 months or pay $240. If you cancel before then, it's $240. Don't do the crime, if you can't do the time. (That's the name o' dat tune.)
You have two choices:
1. Pay the $240. You'll be free and clear to sell your Dish gear, and never look back.
2. Activate one of your boxes (preferably a 301/311 or some other basic box) for AT60 for the remainder of the 12 months. 4 months left? $100 is better than $240. Then, deactivate the 510, and sell it plus any LNB's, switches, other receivers, etc. The one active box need not actually be receiving any programming.