Change of bank accounts

I need to talk to someone in Cell C's credit department as I need to change my debit order from 1 account to another. I don't have time to sit and write emails back and forth. I don't sit in front of my PC all day. Now they tell me they don't have a number to call them to speak to one of their credit department people, which I think is a load of ****. It is a cell PHONE service provider but they don't have a contact number for their credit department. Terrible service isn't even the word for it.