wanting me to pay double

I called in on the 18th requesting an immediate debit on my installment , the consultant advised she cannot do that and advised me to pay it manually and assured me that she will then update my debit order not to be active as I paid earlier . 2 weeks after that I receive an sms saying my account is ion arrears and me paying manually was voluntarily so there fore the debit needs to be honored. Im so frustrated , ho w can I pay double for my account.