Incorrect Billing

I have a contract with vodacom, my upgrade was due so I went and upgraded my contract at the same time I cancelled my insurance on my contract. I was billed for my last contract amount, then the following month billed for the new contract, month after that I was billed double and this month got a different amount again. That's 4 different amounts in 4months. Plus 3 months down the line I find out that my insurance wasn't even cancelled. I want a refund where I got billed double and want the correct amount taken off every month. I've been waiting over a week for someone to get back to me.