[Serusers] Problem with calls

Helo people using ser. I'm havin troubles with my voip calls in the pots sip of my work. We've been using SER like our sip proxy server for severals months. For the office we use Octtel voip gateways that make interal calls and make external calls through a central wich make the conections to the pstn. The las octtels configured can complete the calls but the person that recives the call can't hear me, and if someone call me from anywhere to my line configured in my occtel the same thing happen, l can hear him but he can't hear me. We firts thought that the octtels were the problem, but if i make a call between two lines configured in the same octtel, the call is completed and both, how call and how answer, and viceversa can hear. I'm would like to now if there is any chance that the ser could be doing something wrong, for bad using for someome how up the users account to the SER database, like change configuration, etc.. I'll be grateful for any help or idea you could give me. -- Einar I. González V.