Sling didn't say that, I did . And I have absolutely nothing to do with Sling. In that same message I said to check out https://community.sling.com/thread/3300?tstart=0
Did you do that ? In particular, it said to try all the remotes from that manufacturer, and in this particular case DirecTV always use the same codes so any of their boxes should work. if not the advice was to check IR/RF, Remote Address, camera check....
Did you do any of that ?