Hi Abir,
If you want just the volume of the fibre bundle in terms of the number of voxels intersected, then there is absolutely no need to be interfacing with the afdconnectivity command. The purpose of that command is both to integrate microstructural fibre density information into the quantification (which is not want you want), and to obtain an estimate of fibre bundle cross-sectional area (which has fundamentally different dimensions to volume).
I (eventually) responded to your issues with calculating volume in this thread; I also wrote a little one-liner in another thread for going from a voxel count to a volume in mm3.
Rob