Horror client services from Vodacom

I am very very disappointed with the service from vodacom. This is the worst service I have ever experience. I took up a new contract with them 4 months ago, I had 3 months of horrible services. I have been over billed and everytime I call to query it, I would receive a reference and no call back with an explanation. The last call centre agent I spoke last week, promised me that I would receive a call by yesterday. I have collected a list of reference over the 3 months but no resolution to my query.