Failed to Honor my request to change payment method

On the 11th or 12th January I phoned KingdomBlue requesting for my payment method to be changed from debit order to cash as I will be on unpaid maternity leave, therefore will pay cash. We agreed that the last payment will be 25th January, which went through. The person who assisted me assured me that it has been updated. 26th KingdomBlue tried debiting my account and returned unpaid due to no funds as I advised them. KingdomBlue's customer service is so pathetic, all they know is take ppls money and do not honor what client request. Now i have a negative charges on my account due to their incompetence, I am beyond passed about this.