Vodacom contract

My account was in arears and in march 2018 I went to a Vodacom shop and asked them what is the full amount I need to pay for my account to be cleared and the amount given to me was R 6100.00 and that amount was then paid there and then and was told that the system will keep my phone on a prepaid basis. And all is done (so according to me Vodacom is in breach of contract) as they changed my number to prepaid so I went and got a new number) as there was nothing else to do or say ( contract Cleared) now vodacom want to keep me layeble for full contract and still on ITC for R 6100 what can i do