TELKOM LINE CANCELATION NOT DONE 3 MONTHS LATER

I cancelled my Telkom account beginning of May 2015, the line was cancelled, however, I am still being charged for the line 3 months later. I have asked Telkom for a refund and to please stop billing me, I was assured this would be handled. Now I have just received my next invoice to be deducted 1st September. Do I need to start ******** proceedings against Telkom to have this problem sorted out? In the meantime Telkom sits with my money and who knows how many other people's money, absolutely interest free.