"can not download"...can you expand on that please? What exactly do you try? What exactly happens? Can you download using any other billing methods? If so, then perhaps your carrier does not allow billing through them...of course, only they can answer that question for you.
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.