unresolved Debit order issue

I have a cellphone contract with Telkom that will expire in 7 months. The problem started when I changed my bank details about four months ago and started experiencing terrible service. They debit my account but suspend my cellphone number at the very same time. I've been trying to resolve this issue for two weeks with no success. If I call them, I'll be transferred from one department to another and asked to call different numbers. I discovered that there is only one person(in a big company like Telkom) who deals with debit order queries and who is always not available. I called literally since morning with no luck. This is affecting my work and my credit status.