Me Too!!
It'll work once or twice then not at all. I feel it's a disconnect between the Skill (of which I am finding in general they all are not as good as professed). I've had a lot of problems with Skills, DISH being one, and the developer blames Amazon and Amazon blames the developer and nothing gets fixed.
One place to start is to make sure the DISH Skill is in place and connected to your DISH account, then tell your Echo Device to "Discover my devices" having her go out and hopefully "Discover" your Walley. If there to be discovered, she'll say that she's discovered X number of devices, fingers crossed that the Walley is it or one of them. Then check to see if it's listed in the app by pressing the "House" shaped icon in the lower right corner of the first panel. Then press the "All Devices" button at the top on the right of the row of square buttons. If it's in the list, great you're done discovering it, now on to trying to use it. If not, try pressing the + in the upper right corner of that panel which will slide up a panel at the bottom that has a bar labeled "Add Device" on it. Press that, then it will take you to another confusing panel where you need to scroll down to the bottom, press the "House" like icon that is labeled "Other". This will take you to a panel that has two instructions that you may need to do or should have or could have already done. Now press the bar at the bottom marked "DISCOVER DEVICES" to manually do exactly what you did when asking Alexa to "Discover my devices". The "Light Ring" on your Echo unit should have a dark blue splotch running in a clockwise direction as it did when you asked to do this. Then you will be taken to a panel that will either tell you what it found or that "No new devices have been found" and give you two options below. But if there it will list them. If it's there add the Walley. If not, you're going to have to call a Rocket Scientist for further help. Although, yes, I am one . . . You can call Amazon Echo help and see what they have to say. But if you do the above and they ask you to, tell them you have done this already. Hopefully they will go with that and move on . . .
Once "found" and added to your devices list it should be there to use. "Should" being the operative word.
Since day one with my two Hopper 3's it's been hit or miss controlling them with an Echo device. "It Will Not Work" the way it is advertised. The interaction just isn't there yet. But then there's been times when things are aligned and I make a command and she'll ask do you mean the name of the device that it is under the device "Description" that comes from DISH and not the "Name" that I have gave it listed in "Device Settings" and am under the impression that is what you are suppose to call it. WHICH for some devices is their manufacturer name and serial number. How am I suppose to remember or should need that?!! And even if you say yes to her question it may still not work.
So another part of your problem could be is what name do you use to address the command. Which is it the "Device Name" that you can give it in the settings or the "Description" that the app gets from the device itself that can be a monster? AND what command do I use? It seems to change from day to day what she'll respond to. Sometimes it's a complicated string of words that specifically direct her or I have used something that could be so generic that is could be direct any of a thousand devices, and it works.
I hope my half instructions, half rant is any help to you . . .