Telkom unfair penalties

I have Telkom Mobile account since 2017 and the account is debited monthly with a Debit order. Because my Employer pay us late every month I have requested Telkom to change my debit order date from the LAST day of the month to the 5th of every month. For the past 2 months they still debit the account on the last day which then get returned because of insufficient funds. They then charge me R202.70 for "Payment Rejection Fee" per transaction. I went to the local Telkom shop and spoke to a very unfriendly lady who said the account is in arrears and they will keep on taking the money on the last day until the account is up to date. The DUE date on the statement shows the 5TH but they deduct the money on the 30th or the 31st. The account is NOT in arrears as according to my latest statement (which shows due by 5 July) the amount due is R524.19. The payment is R321.49 and the R202.70 and it totals R524.29. I cannot understand why I should pay them R202.70 because they debit the account on the wrong day. It is not my fault that they make mistakes. The "penalty" is almost 70% of the monthly amount and only because they don't change their info. What Can I do to fix this.......