i terminate a 30 day agreement and they lose it

On the 17 November i terminated my ADSL line with Telkom. Received a termination confirmation that my service would finish on 17 December which was good as we movedd out of the property on the 5th December. I received the normal calls from the retention centre but let them know i was no longer in a Telkom area. In January i received an invoice for 1834 Rand... so i phoned 10210 and after 3 attemots and 51 mins later was informed i had to be transferred to the special accounts department. ..please hold... line went dead. I now receive SMS, s to say my service has been cut off due to non payment. So i now get a bad credit rating and Telkom actually owe me money and have held my deposit... what do you do against such a disgusting service and this can affect my life... Telkom i would like my deposit back i would like my bad credit rating reversed.