Bad service

I had a 24 month contract with cell C for a rooter. The rooter never had network so I was paying for a service I was not able to use. I asked them to cancel the contract after my 24 months was over. They kept on debiting my account then when I called I was told I don't owe any money and they will cancel it. Come month end the depited over R400 and when I asked I was told it's money I owe to them. Bad service this is y I will never have a cell phone contract with any service provider