Over charging or biling

I have contract with Cell c and been receiving crazy bills over the past months.They did not make me aware that the contract was an open line and when i realized that, i requested them to put in a limit of R50p/m. The limit was effected but i still received the crazy bills and i was told its for data usage. Then i requested them to stop the data access but failed to do so. I've been billed R2300 for a R94 contract which i really find redeculas. I tried to make arrangements to pay the bills but somehow ive been called and threatened to be blacklisted though i have stuck to the arrangements. Everytime i talk to cell c they tell me of different outstanding balances. i have requested all the call recording of the conversations i had with them but i am just not winning. i requested the contract to be cancelled and was only contacted after a month to effect the cancellation. ive been charged cancellation fee more than once, ive been billed thousands, ive been threatened and everything that i request is either not done or done late. Can you please assist me in this regard, im not sure what to do anymore, please intervene and advise.