discovery at its worst

My son is a dependent on my medical aid. He has now been employed full time at the same company as I am so now qualifies for his own medical aid. He needs to come off mine and become a main member on his own. Discovery is refusing to let him join a higher plan than what I have as they see these as an upgrade. How does this make sense...he is leaving my plan and joining in his own capacity!! He might as well join Fedhealth on whatever plan he wants.