Line and Services Still Not Cancelled

I am more than furious! I sent a cancellation of our services to Telkom on the 11th February 2016, I have now sent that same cancellation form to the email address I was given. I have sent this request to cancel SIX time in the last month! I have now received an invoice from Telkom for 15 March to 14 April 2016. I refuse to pay the last invoice until it is corrected as I was charged for dates 15 February to 14 March when I have cancelled!! This needs to be sorted out, we are not using the services. On top of that there was NO service from the 2nd February until the end of February. Someone needs to honour my request to have these services CANCELLED with effect from the 11th