Telkom keeps billing me after I cancelled.

I cancelled my account after only using the product (2MB internet adsl) for a month because the speed was rediculously slow at evenings and on weekends (never more than 1.2MB. After cancelling a ricieved sms's saying that my account was in arrears. It is useless to try and contact them because you only get transferred to other departments or there is just never someone at the other end who pics up. Now I am recieving legal notices. All I whant to do is cancel. Why am I paying for internet which I do not even have because the line is suspended? And how can they bill me if it is suspended?