Cannot upload world

I've tried several times to upload a world I had downloaded, only to see a regular minecraft world when I join my server. I'm stumped, and have done just about everything to avoid this problem (renaming the world to "world", checking to see if both the world and server are on the same version [i even tried this with a world that I MADE in the version my sever uses, but the problem still persists], and deleting DIM-1 and DIM1 files in the world folder). Nothing has worked, always a regular minecraft world regardless what world I upload.

Is there a way to fix this? Is this a bug? Is this intentional (if so, why)? Is my world corrupted (i'm almost certain it isn't since it loads fine in singleplayer)?

Thanks in advance

No, it is only 2.8MB when downloaded.

The world was built by me, it was just a superflat void preset with a lobby built in it. I used minecraft version 1.8.9 (the server was in version 1.8). I have not tried using version 1.8 specifically, but I will try it. Software? Does this mean mods or world editing software (like mcedit or worldpainter)?