FALSE ADVERTISING -vodacom direct

I took up a contract with vodacom with a deal of R200.00 a month for the 2 vodafones. Now I'm surprised the bill states I'm supposed to pay R282.00 a month. This is not what we agreed on with the sales consultants. I think these consultants lie to customers in order for them to reach their targets. If a person's contract starts on the 27th of the month, how do you bill them for a full month airtime? Shouldn't it be pro-rata? I would like to cancel this contract because i can't afford the R282 monthly. Please let me know what i need to do to cancel the contract. I don't expect a response that it is already late to cancel the contract. Vodacom knew that by the time I get the invoice it will be late for me to cancel. Now I won't leave this one. And please, stop lying to customers. They are now telling me I cannot cancel the contract because my account is in arrears. These arrears are the undisclosed amounts that I don't even know about. My account has never been in arrears as I pay through debit order.