INCOMPETENCE AND BAD SERVICE!!!!!

Last month Feb i made a payment before my due date because i had changed bank accounts and and immediately phoned Vodacom to advise of this and gave them my new details for future debits. I thought all was well , to my surprise yesterday as i was trying to make a call . I find out my phone is blocked!!!! No warning, No communication, Nothing!!! WHEN I HAVE PAID FOR THE SERVICE and no debit order has gone through on my new account if there was any issue or even the decency of COMMUNICATING with me if there is an issue!!!! I phoned yesterday to find out what the problem is only to be told i am in errears for R180 for the month i have already paid for AT Vodacom and they confirm this. I do not understand WHAT kind of NONSENSE is this!!!!!! AND WHY WOULD They NOt communicate with me if there was an issue, not even an sms. I AM in business and this has affected me a great deal , the useless agent i spoke to could not assist me in any way and therefore i want to Cancel this nonsense contract because I do not understand what more do they want from me when i have paid in full and they admit that and they say its the SYSTEM not them that CUT MY Line!!!! Vodacom you are a not a product of choice and I regret taking this contract in the 1st place. I just need to know how to cancel and move on!!!!!