Data contract cancelled without authorization

I would like to express my dissatisfaction with the customer service have received from Telkom. The day I opened my account, I was told it was a 12 month contract and I signed up for a R99 contract - first deduction came to R107. I actually did not bother to go back to the store to find out what the result was. 1 Year later, I went to the store and asked for a cancellation. The sales person gave me the form to complete and said she would send it to your head office. Two weeks ago I get a call from Telkom confirming the cancellation. She THEN told me that I would be liable for R700.00 seeing as I am ending the contact early. I told her that I signed a 12 month contract. I asked her to send me the contact that I had signed so I can see if this is indeed correct. I asked her to please get back to me and that the matter was unresolved and nothing would be processed - she agreed. 1 December I was debited R107 and the line is disconnected. Telkom does not have my cancellation form and contract on file but yet I have been disconnected. They have also acted without my authorization for the cancellation. Each time I call I am told the matter is being looked into.