Useless Service Provider

I have a contract with Vodacom that is more than 3 years, I have never missed even a single payment, suddenly I'm surprised I'm listed on credit bureau with 1 month in arrears,then I called them to rectify the mistake,I was promised it will updated within 14 to 21 days,I checked again nothing has been done,I'm still listed even today with 1 month behind,I called again was told same story,I'm very upset with Vodacom for damaging my name on credit bureau for no reason,it's the only account that shows payment behind.