Cancelled Contract!!!

Telkom contacted us for an upgrade, we took out the upgrade, but the upgrade was done on the incorrect number and also the contract, we sent back the phone on the 20th of March threw Cell Fix, we are still being charged for the phone after the phone was returned, Telkom debited my account for the phone and on my new invoice the phone still shows, please assist, Selldirect inform me that they did contact Telkom and cancelled the contract, the number must be a pre-paid number but is still an open line!!!!!!!!!!!