I am loosing airtime on my vodacom number continuously even after been assisted by vodacom customer care

My airtime disappears with vodacom, even after being fixed by the previous experts from vodacom. Why must I loose airtime from my vodacom number everytime. I spoke to Pamela from vodacom this morning and she could not help me recover my airtime. Maybe have been using this number for too long and need to get rid of it because I am lost for the way forward.