Incorrect debit day and no communication

So Telkom decides to debit my account on any day it decides, I signed a contract confirming a debit order on the 25th of every month so who said it can debit on the 24th. And this happens with no communication from telkom to say they'll be debiting on a different date. I am not going to pay for telkom's silly mistake of running debit orders on any day they want. And the telkom billing department is just as ridiculous.