Cell C ***** your money!

I have a Top Up Contract with Cell C, which is at a set amount so that I can manage my phone bill in a sensible and responsible manner, I only ported across to Cell C late last year and I even double checked with the Sales Representative that I would only be charged R400.00pm and then once my airtime etc was finished I could top up at my own discretion. However, today I see that Cell C has tried to debit my account of an amount of R439.99, when I called the call centre and queried this, I was told that according to their terms and conditions they were allowed to increase their tariffs at any given time. This is absolutely shocking and disgusting!! I ONLY ever agreed to pay R400 per month and not a cent more!! Cell C, you are such a disappointment and I am going to make sure that everyone I know and more know how you conduct yourselves in business and make sure that I put this onto your Facebook page. Furthermore I will be cancelling my contract with yourselves and I will NOT be paying your cancellation fees! I am one very disappointed customer.