Debit order changes and unfair billing

I made arrangements to change my debit order date twice. Twice it was confirmed changed. Telkom still tried to debit my account on the old date. Of course the debit will bounce. Now they are holding me liable for a "fee" because their agents couldn't do their work properly. Now they are instructing me to go in to their branch because of their negligence. This is extremely disappointing service, especially for such a big provider.