Account over charged due to negligence

I received my Telkom Mobile bill for this month, they billed me an extra R1200 without notifying me why! I went to the Telkom store to find out whats the reason for this. The lady that helped me said she has no authorization to look into my account and gave me te store phone to call 081108. After waiting on the phone for a long while the accounts department said that thy did not bill me for one of my devices the past 3 months, the ammount was R295 pm and even that could not add up to the ammount they wanted to deduct. I said to the lady from the accounts department that they must phone me the following day to make aramgements for the payments or I am going to cancel all of my contracts since they did not keep to the contract I am fully within my rights to cancel all my contracts. It has been almoust a week and they still did not phone me!!!