Contract Cancellation Process

I wanted to get my contract cancelled and converted to prepaid. The official expiry date of said contract was 1 December 2017. On the 23rd November 2017 i called Vodacom cancellations call centre and I was sent a form for premature cancellation together with a quotation. I filled in the form and returned the documents as requested in the form to an email address that appears on the form. When i checked in December my number was still a contract number. I then visited Vodaworld in December - on the 27th - where they checked for me and I was informed that my number will be prepaid from 1 January 2018. Vodacom needs to assure me that my contract has been cancelled and that I will not pay for a service that I did not want for the month of January.