Billed after account has been cancelled

I cancelled my contracts with Cell C in April 2015. Paid the accounts in full as advised by Cell C customer service. In the beginning of May I received a letter from Cell C stating that my account has been paid in full and that the is no outstanding monies owed and that my lines have been moved to prepaid. <br> <br> Low and behold on 15 June 2015 my bank account has been debited for a subscription. After phoning I get told that I must email the person that sent me the letter and I did still no answer. On the phone with the legal department for almost 30 min ***) no answer just playing music in my ear. <br> <br> This is ridiculous, I need someone to contact me immediately to sort this mess out. <br>