Unhappy

I opened a contract with Vodacom and they the did a debit order on my bank account, but then I received a message that the debit order was returned and that I needed to make a payment, I received this message last Saturday but could not make a payment as I was at my works year end function the whole day, So I went the next day to the shop that I got the contract by and the guy said that I can make a payment in store so that I dont get a fine so I did that I made a payment of R306.00 when the amount was actually only supposed to be R305.19, and then I phoned the accounts department on Monday 30.11.2015 to correct my details and the lady told me that I must pay a R100.00 fine. This is not right as it is not my fault that my account details were entered into the system wrongly from day one, I don't think I shouldn't have to pay for something that is not my fault.