Airtime disappearing

Cell C has becomes *******. Airtime keeps disappearing with no explanation from them. In December I recharged and airtime disappeared. When I called the call centre they said they cant see what the airtime was used up for so they will refund the airtime. Still today, no refund was given. Again today, the same thing.... they keep taking the airtime and cant give a reason as to where the airtime was used. Even management don't do anything about it. Seems like this has become a trick for them to make money