MISSING PRE-PAID AIRTIME

My mother, who is in her 80's, bought a new cellphone recently and installed her old pre-paid Vodacom sim card into the new phone. She now has to load R35 of airtime every two or three days, as her airtime keeps disappearing. She very seldom phones, but does send some SMS'e.<br> She has been to the Vodacom shop more than 3 times and nobody can tell her where the airtime is disappearing to. They can't give her a printout, they can tell her if she accidentally subscribed to something. How must she know where the money/airtime goes if VODACOM staff don't know or don't want to help or are just toooo stupid? They are ripping her off with \Passing the Buck\" and I want to know what is going on?????<br> Why does she have to keep going down to Vodacom shops without being sorted out??<br> "