Telkom **** Service demands money!!!

I took out a contract with Telkom for Wi-Fi after cancelling Vumatel. The Sales person assured me that Telkom do not have any network issues in the Delft area, where i reside. 1st month with the wifi, I had endless connectivity problem and contacted them several times and its the one excuse after the other. I work remotely and to be interupted with network outages is not an options. I requested cancellation after the 1st month, and that too has been an endless issue. Finally received an email stating that I must pay Telkom R9980.00 for cancelation. I responded to ask why as I hardly use the wifi in the month. I did not cancel the wifi because i want to I cancelled as they could not provide me with the service promised. No Telkom makes as if my bank account belongs to them by debiting whenever they feel like and sadly sending me SMS and emails non stop of Litigation and Debt Collecting etc. I will not pay for a service i could not make use off. I am now with Rain and am a happy client and pay that account. What can I do please to stop Telkom intimidating a person like this. They literally harassing me.