Cancelled contract

Last year June i went to Southgate Game store and took out 2 iphones on contract. The phones were given to me and sim cards were not activated. After two weeks of struggling with activation, I returned the phones and cancelled the contracts. I received and email from the Game store advising that the contracts were cancelled. Today, I receive and email with a final letter of demand stating that I owe R2 724.70. I tried calling Vodacom today to get assistance as to what this for and keep transferred from pillar to post. I need this resolved ASAP as I am being threatened about being handed over for something which I did not even make use of and confirmation was sent that the contract was cancelled.