How did you try to troubleshoot,
Here comes use of ngrep 
ngrep <DID_NUMBER> port 5060

Follow the output, This to check
1, If you are getting the call on your switch?
2. How is your switch responding to the call? 
3. If everything is fine until here then look in your dialplan. 

 
Jai
www.didforsale.com
*Buy DIDs at low cost unlimited minutes
http://www.didforsale.com"