Wrong Debit Date

So I was debited on the 24 August even though the agreed date was the 25th of each month. Nowhere in the terms and conditions does it state that you can debit the day before if the debit date falls on a Saturday now I'm expected to pay penalty fees, this is not on, its enough that i had to struggle to get my debit date adjusted in the past and pay penalty fees due to Telkom's poor billing system now I'm expected to pay for this as well? Thats not happening