Over billing

I have 2 contracts with cell c, 1 where i get 2G data for R100 and one with a phone plus sim which i pay R400 so in total i should pay R500. Last year my ipad was ****** with the sim in it and i called cell c to block the sim and on my fone I discontinued using the sim because cell c network is so ****ty! What i don't understand is every month I pay R700/800 which i don't understand how because I'm not using any of the sim cards so how can i be charged such a ridiculous amount??? Everytime I call I never get a straight answer. Cell C is just ****ty & dodge. I just want to end these contracts and get my money back!!! I cant be charged R800 for a contract worth R500 and the r100 sim contract i've called 3 times already to cancel it... Still bring charged. I simply hate this network. Never again, i will stll to vodacom, expensive as it is - atleast they are not ******.