Sip user Status for ad hoc

Hello all,
I am having an issue that seems to be fairly comon. I have a Sip device that a user logs into, when a second call comes in the extension rings. I have disabled call waiting, set busy-limit=1 call-limit=2 etc. However no matter what I do I can not prevent the second call from comming in unless I set the call-limit=1 which then prevents the user from making and outgoing call. I am trying to push this system for my work instead of going with a nortell product however I must resolve this before it could be a serious option…
I have found the code that does the dialing, and I know that the sip show inuse shows 1/0 when on a call and 0/0 when not and 2/0 when the second call comes in therefore I would assume that we can check to confirm if a person is already on a call if someone can explain the code to check that status I can mostlikly take care of the rest.
Any help would be great, thanks so much

I am not commenting out the busy-limit and call-limit I ams setting them. I am using Freepbx as the gui in a trixbox build specificaly the latest CE version

What kind of phones are you using ? How are you commenting out busy limit and call limit ? Also are you using any GUI ?

please check above I have added more to this