Telkom is robbing their Clients

I've cancelled my contract on the 27 Feb 2018 and my contracted ended on the 8 March 2018 , i have not heard or received any communication from Telkom now I'm being billed for the month of April since Telkom only cancelled the contracted on the 25th April 2018 why am i being held responsible for the usage of data telkom provided and i want to be refunded this month still. I've spoken to 3 agents telkom on chat saying a case number will be created and im still waiting and to store manager @ blue route mall just sent me an attachment of when it was cancelled