Incorrect Debit Order

Last month Vodacom raised a debit order for half of the amount that they normally collect. In the first week of March I received a notification that my lines would be disconnected if I did not pay the short paid amount of R900. I contacted Vodacom and they said that apparently they had a once off debit order issue so I asked them to raise a debit order for the amount they short collected. I just logged onto my internet banking site to find they did exactly the same thing again, short collecting for about R900. I spoke to a consultant now that wasn't sure if this was correct or not and stated that I should phone the billing department tomorrow. This is not acceptable as I'm the one having to phone around and in all probability will have to, for two months in a row, have to pay for a second debit order fee for an error on their side. Please get someone to phone ME on your debit order issues. After this months error, going forward I will deem debit orders collected as the months full and final settlement of my account. Cannot see why I should have to sort out Vodacoms' debit order problems for them...