Over charging customers

I've been a customer of Vodacom since 2006 and I'm so disappointed by them. For the month of August I had to pay R 1629. 01 that they had to debit but they didn't. Now I called customer service spoke to Cindiswa who put me through to Tracy at the accounts department who now says that when they debited my account they found no money. What surprises me is that I have money in my bank account waiting for them. Now I'm told that I have to pay R 100 for some charge. I will not pay for something that isn't my fault. Vodacom has my banking details and they didn't do their job now I'm to pay more whereas it's not my job to make sure that accounts are debited. This is straight up bull. This needs to be corrected.