If you're loading a savegame where the wall was there upon saving, its not unheard of that its still appears in your game. Sometimes the references for stuff we've removed from cells remain if they're part of the save. I've seen a couple instances of this with my mods.
Load an older save (one created before you added that cell/wall) and go there. If the wall is there, that would be odd.
If all else fails, you can hide it with the console - get close to the wall, press ~ to open console, click the wall (will have a name like 0ed7372596f) and type Disable.