Contract cancelation

I contacted telkom in October to find out when my contract was ending and I was told end of November and I should give 30 days notice for the cancelation of which I did and I won't be debited in December. My contract amount was R139. To my surprise in December telkom debited me R99 while I did everything by the end of October, I then reversed the debit order as I was told that the contract will end in November and I had given 30 days notice. I want to understand, why am I being sent a threatening letter while everything was done on time and I followed the process that I was told to follow by the consultant.