Telkom Mobile Early Debit Underhand Tactics

Early debit order. I have an agreement with Telkom Mobile to Debit my account on the 25th of each month however they attempted to debit my account on Friday 24th August and there was not sufficient funds in my account.The debit order did eventually go off on the 28th August. I have received a statement for September and it states that I have to pay an R200 for missing the debit order. Please note that my contract states that my account should be debited on the 25th and the monthly statement I received from you state Payment due by the 31st August not the 24th? Kindly note that the 25th of Feb & March 2018 was on a Sunday as well.