Custom Contexts applied to a IAX2 trunk

Sorry but the PBX2's routes are managed by another VoIP administrator, so I can't trust him. That administrator is the owner of PBX2, and ?'m from PBX1.

I need a way that let me filter the incoming calls, independently of the route settings in the PBX2 side, and send them where I want (in this case, the IVR extension).

For this reason, I've choosen the Custom Contexts solution, but I've just applied the Custom Context's "context" parameter to the IAX2 trunk's context option, but the calls are still coming to any extension, they are not blocked.

Thanks again, regards!!!