Breach of Contract

I did an upgrade on my existing contract in Feb 2015 before my 24 mnths was due. i called the call centre to get info regarding packages on the item i wanted & to make sure the price of the contract.i was given an amount and went to my nearest branch, which is The Glen. There i was also given the same price on the contract. the amount deducted from my bank account was +- R493 end of March 2015. end of April the amount deducted was R817.10. i went to enquire about this amount, because that was not the amount agreed upon. My contract with Altech clearly stipulates: Migration Date: 23/07/2015 Contract Expiry Date: 12/07/2017.Upon calling the call centre NUMEROUS times last week i was told by markus i need to speak to either Lakrisha Khan,Tom Davids (or someone's name with a C) Collin. i left messages for one of these managers to contact me, to date, NO ONE has called me! i called the call centre back AGAIN today(13 May 2015) and I was told that Lakrisha Khan (according to the lady in the call centre made a note or something on their system) that i should call the branch where i did the upgrade. the glen told me that from 1May Altech changed their contract/billing without notification!