Demands sent after arrangements made

My Account is in arrears. I have made arrangements with the customer care department.. The next day I get an email demanding payment within 2 days.<br> <br> This demand does not conform to the arrangement made with the customer care department. What is the point of making arrangements when you as a supplier does not adhere to the agreement.<br> <br> Sending demands via email and not giving the ability to respond to the email in written is not an acceptable business practice. Is it not good enough that we cannot use the service during the period the arrangements have been made? how can demands be sent when the arrangement is still in place? what wold the NCA have to say about this?