With holding information when upgrading

I just received my account for R200 more than expected - When I called to query it I get told that I upgraded so I am paying for the balance of the previous phone. When I was due for my upgrade I called to query and confirm - I did my upgrade. at NO time did anyone tell me that I would have to pay for extra each month. The service I just got was pathetic - \It is what it is and its not going to change"I have been with Vodacom for 10 years and upgraded more than once and never had to do this"