pay up and upgrade or new contract

This morning I called Vodacom, spoke to Sinalo Dishi. I have been with them for a number of years. I asked them if I could pay up my contract, and then take out a new contract on the same number. The answer was simple, I need to cancel my contract and go on prepaid for 6 months before I can take out a new contract. Nobody at Vodacom can give me a reason, it is there processes that doesn't allow it. I can however cancel the contract and immediately port to another network. They insist this is the way I need to go as they can't accommodate my request. A different network will be able to port my number and give me a contract immediately. I really want to stay loyal to Vodacom, but they have an attitude of you just a number, not a person, we are not willing to accommodate your request.