Constant extra charges on my account!!!

Where to begin! My 2 year contract was finished in January, and yet for February and March i was still being charged for my handset installment. After numerous phone calls, I eventually received a credit note. Now i get my April bill and have been billed a "balance of contract" fee???? I have again called the call centre. I have been told that I was charged this because I haven't cancelled my contract and will continue to be charged this until i do???? I have never in my 25 years with Vodacom ever cancelled, or want to cancel and have never had this issue! The call centre clearly hasn't a clue what they are doing! This has been a never ending story since January. I am now however, considering cancelling after all of this!