Vodacom NOT CANCELLING MY ACCOUNT!

My 2 year contract is over on 24th February 2018 and I had made payment up to the last month on 01 March 2018. Why can't you just cancel my contract without going onto month-to-month. Now I'm in arrears as you put me into month-to-month and you won't cancel my month-to-month until the arrears amount for the month-to-month which I'm NOT even using since I had ported to another network a year ago. If you really want the money, JUST CANCEL my account and I will pay the arrears amount. This is theft. Providing a service which I'm NOT using. JUST CANCEL MY ACCOUNT!