Hello Diane, I'm sorry you are having such a difficult time installing One care. If this has not already been suggested by support I would disable any download accelerator or download manager if present. Since most dial up ISPs provide their own browsers I would temporarily make Internet Explorer the default browser before attempting to install One Care again. Additionally this Microsoft Knowledge Base article may help -
http://support.microsoft.com/kb/934764 Other than that I can only suggest contacting support again and asking to have your support case escalated.
Jim