You can't call that function directly, you need to tell the core to bridge the 2 channels together, or else you end up with 2 threads trying to do media on the same thread.

Look at switch_ivr_uuid_bridge(const char *originator_uuid, const char *originatee_uuid);

Also don't forget to switch_core_session_rwunlock() the session you got out of originate, FS uses reader-writer locks as a reference counting system for session structures, the session thread will do a write lock before freeing the memory. If your call doesn't disappear, you probably are missing that unlock (ivr_originate locks it before returning)