Contract NOT cancelled as requested

Good day, i had a Cell C contract and i phoned in to Cell C to cancell my contract 3 times and i send an email. i phoned in on 18/06/2015 and they said my contract will be cancelled effective 18/07/2015 because of the 30day notice. so they deducted the contract amount and now given me over for bad debt of R 443. but i cancelled it and all fees was paid. i need them to correct this issue as soon as possible.