Contract Cancellation and unauthorized billing

My contract was due to come to end on 26 March and I called customer care notifying them of my intentions to cancel. This was on 13 March. I was informed of the penalty fee which I was amenable to pay and paid same on 15 March. Surprisingly yesterday debited my account twice, and I called their relevant department. I spoke with Kabelo of their retention department who failed dismally to resolve my complaint and promised that I would be phoned by Emma of Billing Department. No one has contacted me and over R900 has been ********ly debited.