Billed when there has been a fault for a month

Telkom has billed me for a service that I have been unable to use for nearly a month. I reported the fault a week ago (3 weeks after it started) and was advised that there was in fact an issue with my line on the exchange. I asked to speak to the billing department who assured me that the service for the period will not be billed for as I was unable to utilize the service. I have subsequently been billed contradictory to the assurance.