Run as a credit card, it should have worked, but would've, could've, should've doesn't matter at this point.
That being said, Dish is my "rebate redemption" site of first choice. Whenever I get a rebate card in the mail, I just log in and pay it on the Dish balance. I'm on auto pay, but there is usually only a few days gap without a balance. Next auto-pay is reduced accordingly. They have taken every one I have thrown at them.
If I don't do it immediately like that it I'm afraid it will end up lost in the back of a drawer somewhere.