Vodacom default payment penalty

I have been a customer for more than 20 years. This month my payment was defaulted due to insufficient funds on the day. When I this on my account, I immediately paid it the following day. (Day after payment was reversed). Now they want to charge me R188 for penalty for what. I checked my contract and did not see anything about penalties listed. I can understand if they are calling after me for weeks to get payment but I literally paid the following day when I received my sms from the bank that evening. I am disappointed by this type of service and will close all my contracts once they come to an end. Loyal customers seem to be non existent at Vodacom.