Ripping people off

I opened a contract with cell c 25 months ago only to have the worst experience ever. I could never phone longer than a few mins before something happens and cut me off. Never use any data due it being too slow, and payed R400 each month wow biggest mistake of my life, so as I know they need a 30 day notice if I would like to cancel so just to be on they safe side I started phoning at 23rd month in the contract and 24th month to cancel as I do not want to be part of cell c any longer than I have to, so they confirmed that it has been cancelled only to find out that the has charged me for a 25th month really. Called them to get told they gave me benefits so if I want to complain I have to call the cancelation center AGAIN really that's just BULL@$#?