Arrogancy and Poor service

I have problem with Cellc, I was not happy with their data service, I decided to cancel the contract, I have followed all the process that they have told me do in order for them to cancel but until today, they haven't cancelled my contract, I have called several times to check if its cancelled, its not done. I have told them that I wont be responsible for the bill of September because the cancellation was done in time. I was told that the cancellation will be done within 24-48 hours, now they are telling me about 72hours after I called to question why still cancellation done. I feel like they do not want me cancel this contract. I am no longer interested to use their data service. Please help me cancel this before month end because I have already cut the budget to Cellc, I wont be accountable for September Bill.