Unauthorized subscription!

We got a call last year asking us if we wanted to be in the yellow pages, upon asking what the charge would be we were told it would be a monthly charge. We declined and said no thank you. We were called numerous times , and we declined each time. They decided to charge us on our Telkom account R538.00 per month for this , we thought it was for our ADSL line at the time as we upgraded speeds, this was not the case. We have sent an email to the cancellations department and our mail was rejected. Now how can we cancel something we have never agreed to no paper ? No one answers the phone and no one comes back to you. Beware of someone phoning you for yellow pages , just decline the call.