VVM Random Debt Collection

VVM sent me an SMS informing me that I owe R1068.10 on my MTN account, and that this has been handed to them to collect.

My MTN account is paid via debit order, and my latest invoice shows that no funds are outstanding longer than 30 days. I have explained this (ad nauseam to the daily call centre operator that contacts me); I have sent them copies of the statement (I copied MTN on that communication); and I have requested repeatedly, verbally and in writing that they explain to me what these funds are for.

Nothing changes - I continue to receive almost daily phone calls to tell me I owe money. As this is unlikely, - I am cautious that this is a **** (I note that this question has been asked of VVM on this platform before) - I remain clueless as to what this money is supposed to be for - I am not prepared to pay anything until reasonable evidence is provided to show me where these costs have been incurred.

This service stinks