over charge on my two Vodacom Mobile Phone Contrac

Vodacom has over charged me on my two mobile phone contracts. Both my cellphone contracts were due for upgrade in August this year. I decided to only upgrade the one phone and not upgrade the other line, therefore keeping my old handset BUT Vodacom is still debiting my account with R199 (x2) for the old handset after the 24 month contracts have expired. Worst of all in the line I upgraded there is an additional R350 I'm paying for the new handset but they are still charging me R199 for the old handset. They sent me confirmation of the upgrades and surely their accounts department should have updated the billing details (amounts accordingly). VODACOM IS RUBBING US AND AFFECTING MY MONTH CASH FLOW. They are not authorised to be debiting me for the R199 x2 and R 33 sms bundle and BBM services after upgrading my contract.