Held Ransom for outstanding amount - Not allowed to cancel

Tried Multiple times to cancel the account 50 GB monthly package, and website will not allow to cancel, they cannot help me over the phone while standing at the clearwater store. Dealing with agents over the phone, they will not assist me. And Telkom will continue to charge for a service that I cannot cancel and not even using, not at the store, or on the website or over the phone. Is this fair?