2004 Pontiac Grand Prix GTP Comp-G

I have been trying to activate an Onstar trial and have been unsuccessful. Every time I hit the button to try connect to a sales rep I get the message, "Cannot connect to Onstar". I've called Onstar and they suggested that I take it to GM and have them diagnosed the problem; which is $100 just to look at it. Any ideas on why this is happening? I've tried moving locations to see if the signal was blocked or something from a building but no luck.