First- you can try carefully dripping some WD-40 around the end of the truss nut- and if it doesn't move in either direction it is stuck (it is also possible that it will spin but go nowhere, which would mean it is stuck AND the rod is broken somewhere inside!). If it will unscrew but not screw tighter, then it is probably maxed out.
If you bought it new, you are entitled to at least have them look at it under the warranty (the 10 years it only applies to the original owner). In this case if you are having a hard time getting ahold of someone, post a detailed description of your problem on this site:
http://www.guitarsbyleo.com/gldp/index.php3
There are a couple important folks from G&L that keep tabs on that forum (well- at least one for sure!)- I had a problem with a new G&L and posted there when I waited months for a return call from the Service Department. Make sure to mention that you have made several attempts to call and email with no luck. I was in email correspondence with both the VP of G&L and the head of the Service Department within a couple days!
Even if you are not the original owner, you should try posting a description of the problem over there- it may still catch the eyes of someone that can help (though generally that forum seems to cater more towards guitarists, their instruments can suffer from the same problems).
Karl