Unhappy customer

My name is Dumisa Mageduka took a broadband contract 10 gig day and 10 gig night at Telkom and was told would pay R139. My debit order date is the 25 of each month in August Telkom decided to go to my bank to debit my account on the 15 don't know why went to my bank to do reversal as they were not supposed to debit that day to my surprise the following month my invoice had an extra R202.70 when I asked about it was told if the debit order bounced you get charged that amount first of all that was not communicated to me when I took the contact because if they did I wouldn't have signed it because how does it make sense to buy and contract of R139 and when u are debited incorrectly u pay more than what you signed for. I called their call centre on the 30 December query number (Telkom SA: Dear Customer, Your query will be attended to.Your case number is ***6Please do not reply to this SMS.) because I told myself I'm not paying that R202.70 so left the R139 only so that they can debit on the 24 Dec however they tried to debit R341.70 because they added that R202.70 so the debit order bounced again and now they added another one meaning the total payment due for this month is R683.40