Changing for cancelled contract

I cancelled a (SIM only) 3G 10 + 10 contract when I took out am LTE contract. This was 2 months ago. When I received my latest invoice the :1 x 10GB + 10GB Internet) is still appearing on my invoice. This was supposed to be cancelled in 30 days. :( Telkom needs to rectify it. Centhia from the Brooklyn branch told me that they made a mistake, because Telkom thought it was contract that needs to be cancelled over a couple of months & not 30 days. No she has called them more then once. She also does not call me back. She said she was going to get them to call me, but it did not happen.