incorrect amount deducted from my account

Hi,<br> I upgraded my cell phone contract last month, June 2015, to a Samsung S6. The contract is R549 per month with a once off top up fee which is R99. On the 23rd June, I received an Mms stating that R1009.33 will be deducted from my account. At the time I wasn't too concerned because as far as I knew, I'm only paying R549 per month. On the 1st July, the R1009.33 was deducted from my account. I went into the Mtn store in Cavendish, where I originally took out the contract, the Manager was no help whatsoever, he told me that there is nothing he can do and that he cant stop the contract, even though they were *********** enough to mess up my contract and the manager kept telling me that I should phone 808 to sort out the issue. The manager couldn't help but he could tell me the exact amount that will be deducted for the month of August. I am very upset and disappointed because i have been a loyal customer for 7 years. I would like to be compensated with interest,this situation inconvenienced my time and my pocket .