Failed to cancel contract

I am highly upset about a request that wasn't followed up. I app**** for a sim and data and upon delivery I cancelled the contract. It stated that i had up to 5 or 7 days to cancel. I did it the very next day as we were getting uncapped from another provider. I sent an email asking how I go about sending the unopened package back but no real answer. I then received a statement saying plus minus R600 will be deducted from my account. I called Mondo who is a partner of telkom and was sent from pillar to post. I sent many emails also. How difficult is it to cancel a contract? You are supposed to be a reputable company and you can't even cancel one lousy contract that is less than R300 a month. I'm sure you are that desperate for the money. The call centres I called were polite... note I mention call centres and not centre.... but they were not sure what they were doing and couldn't give me a clear answer.