It is possible to download the rest of a torrent file.
You only need to copy your partly downloaded file, add your download URL again, pointing it to the same folder where your uncompleted file is saved.
Before you start downloading, please try checking that the peers where you download from are connected.
You can also try downloading the rest of your files from the another trackers. Please, first enable DHT protocol extension (in the Options), start downloading and disable DHT protocol immediately.
Please, also note that some servers do not support download resuming.