Similar problem for me, I can't get past the initial 18gb download. My internet isn't incredibly fast, and I manage to get maybe 12gb in a day before I turn off my computer, then when I turn on my computer the next day it claims nothing I downloaded is still there, and tries to redownload the entire 18gb all over again in an infinite loop.
I have not found a solution or this. I even tried downloading and installing all of the client at a public internet spot then transferring the files to my computer, but the client still completely fails to recognize the files and tries to download the 18gb every time.