billed by trudon for something I never agree to

I phone the telkom call Centre regarding an additional charge on my account, the consultant was unable to help and refered me to the trudon call centre I've since called them twice and the issue has yet to be resolved, seeing that I being charged on my telkom account I expect more action to be taken from their side as my account is with them and they should never have allowed this to happen, how is an account charged for a service that was never agreed to.