Notice to cancel given 19/12/15 yet MTN still bill

I emailed a notice to cancel my service with mtn on the 19 December 2015 to the address provided with my bill ( [Email Removed] Recieved a response back on the 22 December with Appologies for the delay and a promise to esculate the request. Yet nothing is cancelled and a debit order still goes off my account 2 January, to which I email again on the 9 Jan 16 and recieve no response. Please kindly ensure a debit order doesn't go off again this month, refund me for the additional billings and cancel my service.