MTNs Greed

This morning I call MTN to cancel my contract that is coming to an end today and I was told since I pay my account in arrears and have a payment plan in place I cannot, yet on the 1st Frebuary when I called to arrange as I do monthly since my invoice is supposed to be paid on the 2nd of every month and I pay on the 20th . Mtn I cannot afford to pay for the contract anymore I upgraded my modem with you in December is that not enough. I can only take up one contract with you. Please make sure you do not Bill me for my cellphone number as of tomorrow.