Please check below.
Is "Deployment Scanning" part in conf/jboss-service.xml right?
Is Main-Deployer running?
Can you see console messages about deployment when you deploy?
How is your servlet redeployed? Is it packaged in a war file or in an exploded war?
If it is in a war file are you sure that the war was replaced by a later version with a later modified time?
If it is being deployed in an exploded war have you made sure that the web.xml gets updated?