Two things would have worked in your favor. One is you should have been doing your due dilligence and had written down details of the conversation(s) you had with Dish people. Two is you should have recorded the conversations.
Now, do you feel like you should have been a bit skeptical? I other words, did this "promise" to receive a free upgrade to a $700 piece of equipment a bit too good to be true?
Yes, you can say "you trusted this CSR at their word.
Sorry. Not good enough.
UNfortunately the only thing that gets us by these days is documentation.
Hopefully you learned a valuable lesson. If it sounds too good to be true ,it probably is.