2 offices different outbound numbers

Im new to Freepbx and every now and then I have have some troubles... The situation: 2 office with different numbers 2 iax trunks and 2 sip trunks the delivery from the numbers coming in on Sip, no problem Outbound trough IAX, because of some audio problems... Then i have multiple extensions , 10 for 1 office 5 for the other. Now I tried to call out with different numbers but have only succes when I give the extensions the cid of the first trunk, otherwise: all circuits are busy... What am I doing wrong ? Regards Harry Pardon my english im dutch


I inquiring the sollution.
The custom context not good sollution because I allowed the specified outbound route in the custom context the possibilities to call an extension dissapeared.