Contact to prepaid number request from CellC

I had a sim-number that I used for over 10vyears as my prepaid number, 3 years ago I converted it to Cell-C contract and this year I was unable to maintain the contract and CellC closed my line, I now want my sim number back to use as a prepaid as i have been doing it before and as it is the number that all my contacts know, how can I get my number back to prepaid please. Thanks