Xbox 360 won't download games on demand?

Two months ago I purchased Bioshock from games on demand. It began downloading and once it got to 9% it froze and wouldn't continue downloading. I canceled it, deleted it from memory, and cleared my cache and retried it again. The same exact thing happened 6 times before I called Xbox support. They told me to do the same stuff I did. I ended up dropping the call and was never able to download it. Waste of $20. A couple days ago I purchased Need for Speed Shift. It would get to 1% and freeze. I ended up calling again and this time had me recover my gamertag and remove my hardrive. Nothing worked that they tried. The man said I'd be put on the "special case" list and would be contacted in 48 hours. Well no call. I can download everything from add-ons to demos. But for some reason games on demand won't download. Any advice?