Debit Order - ****** money

I changed my banking details with Cell C earlier in the month of April, so that they debit my new account and not the one that they have currently been debiting. I was told four (yes, four) times that the amount would be debited from this new account in MAY only. I clarified this with two different branches, and they said that Cell C will debit the amount from the old bank details end of April, and then debit from the new details ends of May. Cell C has debited from the new account end of April, the opposite of what I was told several times. I did not ensure there were sufficient funds in this account as I knew Cell C would debit the other. Now I am sitting with a negative account balance, and an extra fee of R150 for not having sufficient funds in my account when it was debited ( which is not my fault since Cell C made this error). I'm told in store that they can only reverse it on Tuesday. Reverse the debit order immediately and reimburse me with my bank fees that I incurred due to YOUR mistake. This is unacceptable. If I failed to pay, I'd suffer consequences of being blacklisted and my phone being blocked. I have NEVER failed to pay Cell C, and it is not right to take money where it should not be taken from.