Extra charges that are not my fault

Worst customer service. I have a debit order set for 10th. They decide to debit my account on the 30th, into which I have insufficient funds. Now I pay an extra R145. I email their customer service a few days before the 30th, to ask them not to debit on the 30th because I'll have insufficient funds. They tell me if I cannot mo longer afford the product I should return it. My issue is I set a certaian date on my profile for a reason, then I'm being told they cannot change an active order date, who changed it in the first place? They send me this email with a long list of requirements like payslip and and so they can change my date, obviously I only have one more payment so there's no point anymore. They know what they're doing. Customer service is either stupid or doing this on purpose. Never again.