Vodacom debt collector harassment

A vodacom sales person came knocking to sell fibre lines,his pitch was completely different from what they delivered, when i discovered that they sold me what we didn't agree on I immediately contacted him,he became so rude however when I threatened him he confessed and said he is sorry, the fibre line that was installed never worked as a result I called vodacom to cancel it with immediate effect before the debit order goes off,I am now being harassed by vvm debt collectors on behalf of vodacom saying that my vodacom account is in arrears, I've explained countless times that i don't have an active vodacom line but they still harass me