Cancelled contract but it's still active

On 26.05.2015 I phoned cell c and requested my expired contract to be converted to prepaid. After about an hour on the line Marvin told me that the cancellation request was through and that my line will be converted in 30 Days. (By 1 July). When I checked my balance today, I saw that they loaded airtime again. So my line is not converted. I want the contract cancelled with immediate effect. No waiting 30 days again. Reverse the airtime loaded and also cancel any more deductions from my bank account. I will not pay for July month as I cancelled my contract in time.