Vodacom is trying to ***** from me.

According to my contract with Vodacom my debit order date was for the last day of every month. Vodacom decided without my concent to debit my account on the 29th July instead of the last day of the month and the debit order was not paid. On the last day of th month I did however pay Vodacom in full. Now Vodacom want me to pay a penalty R100.88 because they changed my debit order date without even informing me. I refuse to pay this penalty amount, and if Vodacom cuts my line as a result, the you will lose a customer who pays R2000.00 because you were greedy over R100. This is a matter of principle now and I will not stand by and let Vodacom get away with this dishonest practise.