I still pay for contract that was cancelled

This is my fourth complaint about the same problem. After lodging a complaint on 12 May a Vodacom consultant from Telesales confirmed that my contract will be cancelled. It was not done. First week in July I again lodged a complaint after I was billed for May and June. To this complaint I received no reply from Vodacom. Two weeks later I lodged a 3rd complaint. A consultant contacted me and confirmed the contract will definitely be cancelled. End of July I got billed again for the same contract. I did not use any of the data available on the contract for May, June & July. I did not even have the tablet or simcard in my possession since May but I have to pay for it every month. Vodacom must refund me for the mounts deducted from my account for May, June & July on this contract. I also demand written proof of the contract being cancelled and that no further amounts will be debited.