Vodacom not taking responsibility

When I upgraded my Vodacom contract in Oct 2013, the sales assistant incorrectly loaded the contract information on the system and I was being over charged on my account. The issues was corrected in April 2014, to do this Vodacom cancelled my then contract and started a new one. This changed my upgrade date. Essentially my upgrade date is now Feb 2016, a good few months over the 24 month contract period, if you take it that the actual upgrade was done in Oct 2013. Vodacom told me that I need to contact the store. I did and am still waiting for feedback as of May 2014. It seems that my concerns are falling on deaf ears