Still being charged for services not delivered

Services cancelled in October 2014 still being charged on our account - in spite of being notified in writing, signed by a director of the company. Services requested cancelled end of April 2015 still being charged for. Phone system cancelled as at end April 2015 and requested that the amount be billed monthly until end of contract, charged in full and interest claimed. Dispute declared 21/07/2015 ref ***9 no response from Telkom other than a Letter of Demand. Not only were the services not cancelled when requested, billing was not done as requested.