Vodacom contract

Hello I am currently having a bad experience with vodacom. 2 weeks ago I was billed more than I normally pay. When I called them to find clarification they said I took a recurring Data and airtime advance. I told them I did not take it. I told them they must invistigate because I could be a victim of *****. Nobody come to help me. Now bill is seating on R847. 75 and I normally pay R315. Again this month of I am having a same problem on my other number. Somebody borrowed airtime advance of R98.00. I called vodacom on Monday that my bill is more and I did not borrow any advance. They said they will invistigate they will come back to me. My bill rising every day.