Downloading files on an external hard drive stills decreases the Windows Drive

[Rload]

So basically I was downloading a 11GB size file to my external drive. As time passes, I realize that my Windows drive space decrease a lot, from a 20gb+ space to 8gb. I tried uninstalling the file and utorrent but it doesn't fix it. I tried to find the files that are secretly adding to my Windows Drive but I can't find it. It happens to me a lot now. Please help!