Telkom the company that refuses to solve an account problem for over 12 months

We have been trying to resolve a accounting problem with Telkom for over a year. We cancelled a fixed ADSL line in October 2019 and were charged for 6 months. We then cancelled a second ADSL line in July 2020 and are still being charged. Telkom have handed the account over although they owe us, the client money . You get e-mails from them but can't reply to the e-mail . Thank goodness we don't have to use this typical badly run SOE.