Disgruntled Telkom customer

I have a contract with a Telkom which I took out at the beginning of this year. My debit order goes off on the 25th of every month, however last month Telkom decided to debit on the 24th and when the debit order bounced due insufficient funds they charged me R200 extra whereas our debit order agreement is for the 25th. I called their call center and opened a case. I was told I will be contacted by the finance department within 72 hours which is long gone and passed but still nothing. I have tried calling their call centre to follow up on my query but their lines have been busy.