Telkom is de*****ing people

I have been paying telkom every month by eft and they are busy deducting money from my account even after I have made a payment

They are charging me money for reversing my debit order every month even though I did not give them authorisation to debit my account as I pay it before the due date. They are now sending me sms that my account is overdue even though it has been paid. They dont bother to return calls even when I call. I want all the moneys they have charged since Jan for reversed debit order to be credited to my account as I did if authorise them to debit my account