Account's department RUDE

Received a SMS stating I am in arrears, called them and nobody can tell me what it is for ,as I have a debit order that has never not been paid. I have made numerous calls to them very pointless and more than 3 of the call center personnel dropped the call eventually got through to a supervisor just to receive another message from the account department with the same message and to send proof of payment. No invoice or statement just a demand . Maybe if I was a customer with bad payment history you can act like that but the fact is I am not.