Bully and taking advantage of the customers

I got an sms in December saying that Capfin will deduct that their instalment early in December, and I phoned them notifying them of the fact that won’t be paid by that date and asked if this can be debited on a normal date. They didn’t agree and just said that if I get charged for the debit order bouncing due to insufficient funds I need to send them a statement and they will refund me. I have sent them the statement and the person by the name of Tembela Jim-Qotoyi replying saying that they won’t be refunding me the bank charges. This is all about the principles, the customer must be debited on the date they agreed upon, not as and when Capfin feels like it.