unprofound/false billing

I paid the settlement amount in February,March and April cellc debited my account. I reversed the funds,called them.They told me the contract hadn't been cancelled because I used one mobile as a ref. It took me 2 full months to cancel the contract. Today I receive an sms saying I owe cellc money. Spoke to Tumelo Ndebele the manager who said that its because cellc gave me airtime. But I had called to confirm that they had received funds and they told me they had in the month of february. I spent so much time trying to have the contract cancelled after making the payment and fought with so many agents and today I spoke to the most uncunning and rude agent named Lerato who had me holding for ages only to tell me that I owe them because I used the airtime when I asked her why cellce t me airtime to a cancelled contract line she just asked why I used the airtime so I also tried to explain to the manager/teamleader Tumelo Ndebele who tried to be a coniving advocate and twist my words and have me saying I used the airtime willy nilly. I asked both these people for a paid up letter and both could not assist.