I found out the solution:
When creating the Singleton Service, there are automatically created two child services (ServiceName."service" and ServiceName."singleton"). This services are not removed automatically when removing the parent. THIS ISSUE HAS BEEN SOLVED IN JBOSS 7.1.3 ([AS7-5073] Removing singleton service should also remove child services. - JBoss Issue Tracker)
Since I cannot change the Jboss version I had to find a workaround:
When going to stop the parent service, I take the serviceName variable and I copy it in two new variables. I append each one as follows: serviceNameService.append("service") and serviceNameService.append("singleton") . Then, I use the same code to stop and wait for REMOVED state for the three services.
I get two wanings telling me that the component is already stopped, but it actually works. You can redeploy the EAR without restarting JBoss.