Thats the think, D-Link sold there router HW to 3rd party vendors and ISPs which used there own developed FW on it. Those parties developed and maintained there own FW, not D-Link.
After there FW is loaded on it, it would have to be updated by DISH. I presume since DISH may not support this any longer, whom ever you bought it from didn't know the differences now did you. So, either the router needs to be sent back or you can try doing the recovery process and this time if you can get the recovery mode screen to come up, it may accept D-Link OEM FW. There is a chance it may not. Up to you.