You can’t cancel a Telkom contract

I have been battling to cancel my Telkom line for over a year now. I was in a 24 month contract, the contract lapsed. I went online to cancel my internet 9 months after my Telkom contract ended. They continued to bill me for an additional 3 months. I do not understand why since they had confirmed that my contract was cancelled. Now they have sent me a bill of over R1200 for an account that was confirmed to be closed in July 2019. I am extremely disappointed in the way they conduct business and rob clients of their money.