Over Charged Bill

I have been a Vodacom customer for close to 5 years and all I've ever done is endure bad service, i called into the network as i had seen a change in my billing account and saw a difference of R450 on my bill which i did not agree to. I called in only to be told that a reference number has been created, i never heard from them again only for this new amount to be debited from my account. again i called in re this query and the agent dropped the call on me.. i dont know what length i need to go into further as i am met with little to no assistance.. i want to end my contractual agreement with the company as all they do is take and never make sure the customer is receiving adequate service. I want a refund and to change networks with immediate effect