Contract closed in advance

I paid up my account and told them to close my account, my contract with cell C was R 199 p.m , I paid it up inadvance so that incase I forgert to send a letter to close. They just moved my account to prepaid but now I paid for services like my free minutes and data that I supposedly forfeited, this is not the first time cell c is cheating me, that is why I will never take out a contract with them or even renew my contract I want my free minutes and my data that I paid for as my contract was only supposed to be stopped on the 13 April 2016, what happens to my data and free minutes for the three months. Contract number ***