Fortivoice Outgoing call not working

I have fortivoice enterprise 300 E-T. I have configure office peer (SIP-TRUNK) with my IPTSP service provider which works fine. The IPTSP provider give me bunch of DID number and I have local 6 digit extension (2110XXX)number. When I call from my mobile to the DID (09612110XXX) number I received call to my local extension and it works fine. But when I call from my local extension the mobile number it doesn't work, call just hangup or wait for sometime then hangup. IPTSP end server gets request directly from my local extension (2110XXX). The request should be go using DID not internal number. Can anybody help me to solve the issue?