Contract cancelation

I have had a contract with vodacom for 36 months. My contracted just ended and I want to cancel the R280 per month sim card upgrade to prepaid as I don't need the data or call minutes. I have called 3 times and I still don't have a cancelation confirmation. The 3rd I called I was told I have to pay more to take my simcard to prepaid this makes no sense. I then wake up and go to the store to see if I can get assistance. A whole vodacom store can't cancel your contract and change your number to prepaid. I have to call the same landlines number where they don't want you to cancel qnd keep throwing you options that don't make sense. Please cam someone from vodacom just cancel the contract that I have completed paying.