Debit order rejection fee

I have been a customer for around 4 years. I have always done EFT payment with no issues. Lately (during lock down specifically) I have been charged a debit order rejection fee. Even though i have always paid them via EFT every single month like clock work. In June they credited the fees with no hassles. For august they refuse to credit it even though they send you a invoice thanking me for my payment on the 19th of Aug and charging me the rejection fee on the 22 Aug. I called the customer services and the agent blatantly refuse to credit it saying the previous agent made a mistake and saying i need to do the cash payment 10 days before debit order date even though i haven't setup such date at all. I am still waiting for a manager to call me 3 days later. What makes me sad is i have been a loyal customer for the past 4 years never missing a payment . I have subsequently sent in a online request to cancel my contract and yes you guest it, no one has call me yet