Absolute Ignorance and total disregard for its' customers

My son has been trying for more than 18 months to get his data-contract with Telkom cancelled. Visiting the Telkom branches in the Doornpoort area, telephoning the help centres and E-mailing the accounts department just does not help. The worst of it all is that every month he receives an updated account which includes the supposed amount payable for using the data on the contract the previous month. How the heck do we get rid of this useless contract - and - without paying for anything since the contract has elapsed??