Customer Harassment

Their service is really bad. I had a contract with them and it ended this year June. To my surprise, I get a call telling me that Telkom has handed me over to be blacklisted. I was so furious I called the customer care to let them know I don't understand why I owe them whilst the contracted has ended. I asked for my query to be escalated and I was told the I will receive a call from the manager. till to date, I have had nothing from them but I still get messages about my account been in arrears.