Still being invoiced for a closed account

I cancelled my line ***) on the 30th April 2015 with reference number ***A. The 30 day notice period meant the line would be cancelled on the 30th May 2015. The line went dead at midnight on the 30th May 2015 - Well done Telkom!<br> <br> But I'm still getting billed for this line even though the account was settled fully at the time of cancellation. I've reported this on Telkom's escalation center on the 12 June 2015 and again on the 28th July 2015 - but still no feedback from Telkom. Not even a call or an email to confirm that the account has been closed!<br> <br> Please close the account once and for all !