Refusal of contrcact cancellation on agreed date

I called in today 05/03/2015 to cancel my 24 months cellphone contract with Virgin Mobile SA as I was advised by a customer service consultant late January 2015 when I called in to enquire about the cancellation date and process. To my surprise,the gentleman I spoke to on the phone stated that he will only cancel my contract effective April 2015 because I failed to give a month's notice for the cancellation. So when I tried explaining to this guy that I did call on a certain date in January (which he als confirmed as per their records), he told me that Call centre gents know nothing about cancellations!!! Puzzled and rather rattled as I was to hear such an appauling response, I gave him a history of the nature of calls I have been making regarding this cancellation since last year where I was first told to write a letter 30 days prior to the termination date, when I called to find out which email address must I send it to I was told I must just call on the day of cancellation and just cancel without a hassle. I was surprised to get such feedback when trying to cancel today and I'm not willing to pay a single dime towards Virgin Mobile after today because I HAVE CANCELLED.