Telkom bad service

I took out a contract for a mobile rooter paid for 24 months without skipping one installment. Required an upgrade with no reply. When I cxd my debit order I was told that I am not allowed to cancell the debit order but Telkom also don't want to stop the contract all though it already exp in March 2021. According to Telkom I need to register on line to stop the contract but when it was opened 2 years ago there was no need to register online. I want this contract cancelled as it is paid up and never ever want anything from Telkom again.