Telkom gives very good service, though debiting me a day earlier than agreed on, is very bad

I got an SMS from Telkom, that they'll be debiting my account on Friday, the 24th. One day earlier, than agreed upon. This effectively means, that I'll be going on over-draft and will be charged interest. Meanwhile, all my other debits will go off on the 25th or on Monday the 27th. Why can't Telkom also just wait till Monday, if they don't want to debit on Saturdays? Guy on their helpline, wasn't very helpful. Just said it's to late now, order has already been put. Didn't offer a solution for future debits.

I ask for one of two things: Fix the debit date on future debits or Change all my existing, month to month contracts to pay-as-you-go.

Over-all experience with Telkom Mobile is very positive, just this negative tick on the list that's gonna give my bank and maybe creditors a negative view of me.